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HAEMOSPORIDIA

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Originally appearing in Volume V12, Page 811 of the 1911 Encyclopedia Britannica.
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HAEMOSPORIDIA , in See also:

zoology, an See also:order of See also:Ectospora, which although comparatively few in number and very inconspicuous in See also:size and See also:appearance, have of See also:late years probably attracted greater See also:attention and been more generally studied than any other See also:Sporozoa; the See also:reason being that they include the See also:organ-isms well known as malarial parasites. In spite, however, of much and careful See also:recent See also:research—to a certain extent, rather, as a result of it— it remains the See also:case that the Haemosporidia are, in some respects, the See also:group of the Ectospora about which our knowledge is, for the See also:time being, in the most unsatisfactory See also:condition. Such important questions, indeed, as the See also:scope and boundaries of the group, its exact origin and See also:affinities, the See also:rank and interclassification of the forms admittedly included in it, are answered quite differently by different workers. For example, one well-known Sporozoan authority (M. Luhe) has recently See also:united the two See also:groups, Haemosporidia and Haemoflagellates, bodily into one, while others (e.g. Novy and McNeal) deny that there is any connexion whatever between " Cytozoa " and See also:Trypanosomes. Again, the inclusion or exclusion of forms like Piro plasma and Halteridium is also the subject of much discussion. The See also:present writer accepts here the view that the Haemosporidia are derived from Haemoflagellates which have See also:developed a gregariniform (Sporozoan) phase at the expense, largely or entirely, of the flagelliform one. The not inconsiderable See also:differences met with among different types are capable of explanation on the ground that certain forms have advanced farther than others along this particular See also:line of See also:evolution. In other words, it is most probable that the Haemosporidia are to be regarded as comprising various parasites which represent different stages intermediate between, on the one See also:side, a Flagellate, and on the other, a typical chlamydospore-forming Ectosporan See also:parasite. While, however, it is easy enough sharply to See also:separate off all Haemosporidia from other Ectospora, it is a very difficult See also:matter to define their limits on the former side. Two See also:principal criteria which a doubtful haemal parasite might very well be required to satisfy in order to be considered as a Haemosporidian rather than a Haemoflagellate are (a) the occurrence of schizogony during the " corpuscular " phase in the Vertebrate See also:host, and (b) the formation of many germs (" sporozoites ") from the zygote; so See also:long as these conditions were complied with, the present writer, at all events, would not feel he was countenancing any protozoological See also:heresy in allowing for the possibility of a Flagellate (perhaps trypaniform) phase or features being present at some See also:period or other in the See also:life-See also:cycle.' To render this See also:article See also:complete, however, one or two well-known parasites, hitherto referred to this order, must also be mentioned, which, judged by the above (arbitrary) See also:standard, are, it may be, on the Haemoflagellate side of the dividing line (e.g.

Halteridium, according to Schaudinn). - The See also:

chief characters which distinguish the Haemosporidia from other Ectospora are the following. They are invariably See also:blood parasites, and for See also:part or all of the trophic period come into intimate relation with the cellular elements in the blood. There 'Compare, for example, the flagellated granules of certain Coocidia, which point unmistakably to a Flagellate ancestry.is always an See also:alternation of hosts and of generations, an In-vertebrate being the definitive host, in which sexual conjugation is undergone and which is to be regarded as the See also:primary one, a Vertebrate being the intermediate or secondary one. The zygote or sporont is at first capable of See also:movement and known as an ookinete. No resistant spores (chlamydospores) are formed, the ultimate germs or sporozoites always being See also:free in the oocyst and not enclosed by sporocysts. To See also:Sir E. See also:Ray Lankester is due the See also:honour of discovering the first Haemosporidian, a See also:discovery which did not take See also:place until after most of the other kinds of Sporozoa were known. In 1871 this author described the parasite of the See also:frog, which he later termed Drepauidium ranarum. The next discovery was the See also:great and far-reaching one of Laveran, who in 1883 described all the characteristic phases of the malarial parasite which are met with in human blood. While regarding the organism as the cause of the disease, Laveran did not at once recognize its See also:animal and Sporozoan nature, but considered it rather as a See also:vegetable, and termed it Oscillaria malariae. As in the case of the Trypanosomes, we owe to Danilewsky (1885–1889) the first serious attempts to study the See also:comparative See also:anatomy and life-See also:history of these parasites, from a zoological point of view.

Danilewsky first named them Haemosporidia, and distinguished between Haemocytozoa and Leucocytozoa. To the brilliant researches of R. See also:

Ross and Grassi in the closing years of the 19th See also:century is due the realization of the essential part played by the See also:gnat or See also:mosquito in the life-cycle and transmission of the parasites; and to MacCallum belongs the See also:credit of first observing the true sexual conjugation, in the case of a Halteridium. Since then, thanks to the labours of Argutinsky and Schaudinn, our know-ledge of the malarial parasites has steadily increased. Until quite recently, however, very little was known about the Haemosporidia of See also:cold-blooded Vertebrates ; but in 1903 Siegel and Schaudinn demonstrated that the same role is performed in their case by a See also:leech or a tick, and since then many new forms have been described. The Haemosporidia are widely distributed and of very See also:general occurrence among the chief classes of Vertebrates. Among In-vertebrates they are apparently limited to blood- occur. sucking See also:insects, See also:ticks and leeches.' As already stated, rence; the universal See also:habitat of the parasites in the Vertebrate habitat; is the blood; as a result, of course, they are to be met effects on with in the capillaries of practically all the important host. See also:organs of the See also:body; and it is to be noted that while certain phases (e.g. growing trophozoites, mature gametocytes) are found in the peripheral circulation, others (e.g. schizogonous " rosettes," See also:young gametocytes) occur in the See also:internal organs, See also:liver, kidneys, &c., where the circulation is sluggish. The relation of the parasites to the blood-cells varies greatly. Most attack, probably exclusively, the red blood corpuscles (haematids); a few, how-ever, select the leucocytes, and are therefore known as Leucocytozoa. In the case of Mammalian and Avian forms (malarial parasites) Schaudinn and Argutinsky have shown that the trophic and schizogonic phases are not really endoglobular but closely attached to the corpuscle, hollowing out a depression or space into which they nestle; the gametocytes, on the other See also:hand, are actually intercellular. Forms parasitic in cold-blooded Vertebrates, on the contrary, are always, so far as is known, endoglobular when in relation with the corpuscles; and the same is apparently the case with the Mammalian parasite, Piroplasma. Although in no instance so far described is the parasite actually intranuclear (as certain See also:Coccidia are), in one or two cases (e.g.

Karyolysus of lizards and certain See also:

species of Haemogregarina) it reacts markedly upon the See also:nucleus and soon causes its disintegration. While many Haemosporidia (e.g. malarial parasites, with the exception of Halteridium) remain in connexion with the same corpuscle throughout the whole period of growth and schizogony, the new See also:generation of merozoites first being set free from the broken-down See also:cell, others (the Haemo- ' A possible exception is a doubtful species of Haemogregarina, which has been described from the walls of the blood-vessels of an. Annelid. See also:gregarines, broadly speaking, and also Halteridium) leave one corpuscle after a See also:short time, wander about free in the plasma, and then seek out another; and this may be repeated until the parasite is ready for schizogony, which generally occurs in the corpuscle. As in the case of Trypanosomes (q.v.), normally—that is to say, when in an accustomed, tolerant host, and under natural conditions—Haemosporidia are non-pathogenic and do not give rise to any See also:ill-effects in the animals harbouring them. When, however, the parasites gain an entry into the blood of See also:man or other unadapted animals,' they produce, as is well known, harmful and often very serious effects. There are three recognized types of malarial See also:fever, each caused by a distinct See also:form and characterized by the mode of manifestation. Two, the so-called benign fevers, are intermittent; namely, tertian and quartan fever, in which the fever recurs every second and third See also:day respectively. This is due to the fact that schizogony takes different lengths of time in the two cases, 48 See also:hours in the one, 72 in the other; the height of the fever-period coincides with the break-down of the corpuscle at the completion of the See also:process, and the liberation of great See also:numbers of merozoites in the blood. The third type is the dangerous aestivo-autumnal or pernicious See also:malaria, in which the fever is irregular or continuous during long periods. A very general symptom is See also:anaemia, which is sometimes present to a marked extent, when it may See also:lead to a fatal termination. This is the result of the very considerable destruction of the blood-corpuscles which takes place, the haemoglobin of which Is absorbed by the parasites as nutriment.

A universal feature connected with this mode of See also:

nutrition is the See also:production, in the cytoplasm of the parasite, of a See also:brown pigment, termed melanin; this does not represent reserve material, but is an excreted bye-product derived from the haemoglobin. These pigment-grains are at length liberated into the blood-stream and become de-posited in the various organs, See also:spleen, liver, kidneys, See also:brain, causing pronounced pigmentation. Another type of fever, more acute and more generally fatal, is that produced by forms belonging to the genus Piro plasma, in See also:cattle, See also:dogs, horses and other domestic animals in different regions of the globe; and recently See also:Wilson and Chowning have stated that the " spotted fever of the Rockies " is a human piroplasmosis caused by P. hominis. The disease of cattle is known variously as See also:Texas-fever, Tristeza, Red-See also:water, See also:Southern cattle-fever, &c. In this type of illness the endogenous multiplication of the parasites is very great and rapid, and brings about an enormous diminution in the number of healthy red blood corpuscles. Their sudden destruction results in the liberation of large quantities of haemoglobin in the plasma, which turns deep-red in See also:colour; and hence haemoglobinuria, which occurs only rarely in malaria, is a See also:constant symptom in piroplasmosis. The parasite of pernicious malaria, here termed Laverania malariae, will serve very well as a type of the general life-cycle (fig. r). Slight differences shown by the other malarial parasites (Plasmodium) will be mentioned in passing, but the Example See also:main divergences which other Haemosporidian types of the life- history. exhibit are best considered separately. With the bite of an infected mosquito, the See also:minute sickle-like sporozoites are injected into the blood. They rapidly penetrate into the blood corpuscles, in which they appear as small irregular, more or less amoeboid trophozoites. A vacuole next arises in the cytoplasm, which increases greatly in size, and gives rise to the well-known, much discussed See also:ring-form of the parasite, in which it resembles a signet-ring, the nucleus forming a little thickening to one side. Some authorities (e.g.

Argutinsky) have regarded this structure as being really a greatly distended vesicular nucleus, and, to a large extent, indeed, an artifact, resulting from imperfect fixation; but Schaudinn considers it is a true vacuole, and explains it on the ground of the rapid nutrition ' For an interesting See also:

account of the biological relations between parasites and their hosts, and the See also:penalty Man pays for his roving propensities, the reader should see Lankester's article in the Quarterly See also:Review, See also:July 1904.and growth. Later on this vacuole disappears, and the grains of pigment make their appearance. The trophozoite is now large and full-grown, and has become rounded and ready for schizogony. The nucleus of the schizont divides several times (more or less directly, by See also:simple or multiple fission) to form a number of daughter-nuclei, which take up a See also:regular position near the periphery. Around these the cytoplasm becomes segmented, giving rise to the well-known See also:corps en rosace. Eventually the merozoites, in the form of little See also:round uninuclear bodies, are liberated from the now broken-down corpuscle, leaving behind a certain amount of residual cytoplasm containing the pigment grains. Besides the difference in the time taken by the complete process of schizogony in the various species (see above), there are distinctions in the See also:composition of the rosettes. Thus, in Laverania, the number of merozoites formed is very variable; in Plasmodium vivax (the tertian parasite) there are only few (9 to 12) merozoites, but in P. malariae (the quartan form) they are more numerous, from 12 to 24. The liberated merozoites proceed to infect fresh blood corpuscles and a new endogenous cycle is started. After asexual multiplication has gone on for some time, sexual forms become developed. According to Schaudinn, the stimulus which determines the production of gametocytes instead of schizonts is the reaction of the host (at the height of a fever period) upon the parasites. A young trophozoite which is becoming a gametocyte is distinguished from one which gives rise to a schizont by its much slower See also:rate of growth, and the See also:absence of any vacuoles in its cytoplasm.

The gametocytes themselves are characterized by their See also:

peculiar shape, like that of a sausage, whence they are very generally known as " crescents." Male and See also:female gametocytes are distinguished (roughly) by the arrangement of the pigment-grains; in the former, they are fairly evenly scattered throughout the cytoplasm, but in the megagametocytes the pigment tends to be aggregated centrally, around the nucleus. As they become full-grown and mature, however, the gametocytes lose their crescentic form and assume that of an See also:oval, and finally of a See also:sphere. At the same time, they are set free from the remains of the blood corpuscle; The spherical See also:stage is practically the limit of development in the Vertebrate host, although, sometimes, the nucleus, of the microgametocyte may proceed to See also:division. The " crescents " of, the pernicious parasite afford a very important diagnostic difference from the gametocytes of both species of Plasmodium, which have the See also:ordinary, rounded shape of the schizonts. In the case of the latter, points such as their slower growth, their less amoeboid See also:character, and their size furnish the means of distinction. When a gnat or mosquito sucks blood, all phases of the parasite in the peripheral circulation at that point may succeed in passing into the See also:insect. If this occurs all trophic and schizogonic phases are forthwith digested, and the survival of the sexual phases depends entirely upon whether the insect is a gnat or mosquito. Only in the latter case can further development of the gametocytes go on; in other words, only the genus Anopheles, and not the genus Culex, furnishes specific hosts for the malarial parasites. This is a biological fact of considerable importance in connexion with the prophylactic See also:measures against malaria. In the See also:stomach of an Anopheles, the gametocytes quickly proceed to gamete-formation. The nucleus of the microgametocyte divides up, and the daughter-nuclei pass to the periphery. The See also:surface of the body grows out into long, See also:whip-like processes, of which there are usually 6 to 8 (probably the typical number is 8); each is very motile, in this respect strongly resembling a flagellum.

This phase may also develop in See also:

drawn blood, which has, of course, become suddenly cooled by the exposure; and it seems evident that it is the See also:change in temperature, from the warm to the cold-blooded host, which brings about the development of the actual sexual elements. Earlier observers regarded the phase just described as representing another parasite altogether, of a Flagellate nature—whence the well-known See also:term, Polymitus-form; and even more recent workers, such as Labbe who connected it with the malarial parasite, failed to appreciate its true significance, and See also:con. sidered it rather as a degeneration-appearance. The micro-gametes soon liberate themselves from the residual cytoplasm of the See also:parent and swim away in See also:search of a megagamete; each. is a very slender, wavy filament, composed largely of See also:chromatic substance. The finer details of structure of the microgamete of a malarial parasite cannot be said, however, to be thoroughly known, and it is by no means impossible that its structure is really trypaniform, as, according to Schaudinn's great See also:work, is the case with the merozoites and sporozoites. The megagametocyte becomes a megagamete directly after a process of maturation, which consists in the See also:expulsion of a certain amount of nuclear substance. The actual conjugation is quite similar to the process in Coccidia, and the resulting zygote perfectly homologous. In the present case, however, the zygote does not at once secrete an oocyst, with a thick resistant See also:wall; on the contrary, it changes its shape, and becomes markedly gregariniform and active, and is known for this reason as an ookinete. The ookinete passes through the See also:epithelial layer of the stomach, the thinner and more pointed end leading the way, and comes to See also:rest in the connective See also:tissue forming the See also:outer layer of the stomach-wall (fig. 2). Here it becomes rounded and cyst-like, and grows considerably; for only a thin, delicate cyst-membrane is secreted, which does not impede the absorption of nutriment. Meanwhile, the nucleus has divided into several, 01 . Aft.

From Lankester's See also:

Treatise on Zoology. oes, See also:Oesophagus. Mt, M a 1 p i g h l a n st, Stomach. tubules. cy, Cysts. int, See also:Intestine. around each of which the cytoplasm becomes segmented. Each of these segments (" blastophores," " zoidophores ") is entirely comparable to a sporoblast in the Coccidian oocyst, the chief difference being that it never forms a spore; moreover the segments or sporoblasts in the oocyst of a malarial parasite are irregular in shape and do not become completely separated from one another, but remain connected by thin cytoplasmic strands. Repeated multiplication of the sporoblast-nuclei next takes place, with the result that a great number of little nudei are found all round the periphery. A corresponding number of See also:fine cytoplasmic processes grow out from the surface, each carrying a nucleus with it, and in this manner a n, Nucleus of the parasite. p, Melanin pigment. fl, " Flagella." sp. bl., Sporoblasts. r. n., Residual nuclei. r. p., Residual protoplasni. From Lankester's Treatise on Zoology.

I.-V. and 6-Io show the schizogony. VI.-XII., The sexual generation. I.-III., Young amoebulae in blood-corpuscles. IV., Older, actively amoeboid trophozoite. V., Still older, less amoeboid trophozoite. 6, Mature schizont. 7, Schizont, with nucleus dividing up. 8, Young rosette stage. 9, Fully formed rosette stage. Merozoites free in the blood by breaking down of the corpuscle. VI., Young indifferent gametocyte. IX., a and b, Spherical gametocytes; in the male (IX. a) the nucleus has divided up.

X., a and b, Formation of gametes; in the male (X. a) the so-called flagella or male gametes (fl) are thrown out, one of them is seen detached; in the female (X. b) a portion of the nucleus has been . expelled. XI., A male gamete penetrating a female gamete at a See also:

cone of reception formed near the nucleus. XV., Commencing multiplication of the nuclei in the occyst. XV I II ., Full-grown occyst crammed with ripe sporozoites; on one side the cyst has burst and the sporozoites are escaping. a, b, c, a b c. d. e f From Lankester's Treatise on Zoology. (After Laveran, magnified about 1800 diameters.) huge number of slender, slightly sickle-shaped germs or sporozoites (" blasts," " zoids," &c.) are formed. Each oocyst may contain from hundreds to thousands of sporozoites. When the sporogony (which lasts about so days) is completed, the oocyst ruptures and the sporozoites are set free into the body-cavity, leaving behind a large quantity of residual cytoplasm, including pigment grains, &c. The sporozoites are carried about by the blood-stream; ultimately, however, apparently by virtue of some chemotactic attraction, they practically all collect in the salivary glands, filling the secretory cells and also invading the ducts. When the mosquito next bites a man, numbers of them are injected, together with the minute drop of saliva, into his blood, where they begin a fresh endogenous cycle. There is only one other point with regard to the life-history that need be mentioned. With the See also:lapse of time all trophic and schizogonic (asexual) phases of the parasite in the blood See also:die off.

But it has long been known that malarial patients, apparently quite cured, may suddenly exhibit all the symptoms again, without having incurred a fresh infection. Schaudinn has investigated the cause of this recurrence, and finds that it is due to the See also:

power of the megagametocytes, which are very resistant and long-lived, to undergo a See also:kind of parthenogenesis under favourable conditions and give rise to the ordinary asexual schizonts, which in turn can repopulate the host with all the other phases. Microgametocytes, on the other hand, die off in time if they cannot pass into a mosquito. Various types of form are to be met with among the Haemosporidia. In one, characteristic of most (though not of absolutely Compares• all) parasites of warm-blooded Vertebrates, the tropho-Co pars zoites are of irregular amoeboid shape; hence this See also:section dire M ppnoior- ,ogy, is generally known as the Haemamoebidae. In another See also:variations type, characteristic of the parasites of cold-blooded la the life- Vertebrates, the body possesses a definite, vermiform, i.e. cycle where gregariniform shape, which is retained during the intrakaown. corpuscular as well as during the free condition; this section comprises the 'Haemogregarinidae. Allied to this latter type of form are the trophozoites of Piroplasma, which are normally See also:pear-shaped; they differ, however, in being very minute, and, moreover, exhibit considerable polymorphism, See also:rod-like (so-called bacillary) and ring-forms being of See also:common occurrence. It is important to See also:note that in a certain species of Haemogregarina (fig. 3) The form of the parasite found free in the blood-plasma. Parasite within a blood-corpuscle, preparing for division; the nucleus has already divided. The parasite has divided into two rounded corpuscles, the young trophozoites markedly resemble Piroplasma in their pyriform appearance; and a further point of agreement between the two forms is mentioned below. Lastly there is the Avian genus Halteridium, the trophozoites of which are characteristically See also:bean-shaped or reniform.

True Haemogregarines also differ in other slight points from " Haemamoebae." Thus the young endoglobular trophozoite does not exhibit a ring (vacuolar) phase; and the cytoplasm never contains, at any period, the characteristic melanin pigment above noted. In some species of Haemogregarina the parasite, while iatracorpuscular, becomes surrounded by a delicate membrane, the cytocyst; on entering upon an active, " free " period, the cytocyst is ruptured and See also:

left behind with the remains of the corpuscle. A very interesting cytological feature is the occurrence, in one or two Haemosporidia, of nuclear dimorphism, i.e. of a larger and smaller chromatic body, probably comparable to the trophic and kinetic weld of a Trypanosome; or of the " Leishman-See also:Donovan " bodies. Schaudinn was the first to See also:notice this character, in Piro-plasma canis, and his observation has since been confirmed by Luhe.' Moreover, Brumpt has also noticed nuclear dimorphism in the ookinete of a species of Haemogregarina in a leech (as the Invertebrate host)—a highly important observation. As regards the life-history, the endogenous (schizogonous) cycle is known in many cases. Sometimes schizogony takes the See also:primitive form of simple binary (probably) See also:longitudinal fission; this is the case in Piroplasma (fig. 4) and also in Haemogregarina bigemina just referred to. From this result the pairs of individuals (" twins ") so often found in the corpuscles. In addition, however, at any rate in Piroplasma, it is probable that multiple division (more allied to ordinary schizogony) also takes place; such is the case, according to Laveran, in P. equi, and the occurrence at times of four parasites in a corpuscle, arranged in a cruciform manner, is most likely to be thus explained. Labbd has described schizogony in Halteridium From Lankester's Treatise on Zoology. in the blood-corpuscles of the ox. (After Laveran and Nicolle.) a, Youngest form. g, h, i, j, Various forms of the b, Slightly older. twin parasite.

c and d, Division of the nucleus. k and 1, Doubly infected See also:

cor- e and f, Division of the body of puscles. the parasite. danilewskyi as taking place in a rather peculiar manner; the parasite becomes much drawn-out and halter-like, and the actual division is restricted to its two ends, two clumps of merozoites being formed, at first connected by a narrow strand of unused cytoplasm, which subsequently disappears. Some doubt, however, attaches to this account, as no. one else appears to have seen the process. For the rest, schizogony takes place more or less in the customary way, allowing for variations in the mode of arrangement of the merozoites. It remains to be noted that in Karyolysus lacertarum, according to Labbe, two kinds of schizont are developed, which give rise, respectively, to micromerozoites and megamerozoite', in either case enclosed in a delicate cytocyst. This probably corresponds to an See also:early sexual differentiation (such as is found among certain Coccidia (q.v.), the micromerozoites producing eventually micro-gametocytes, the others megagametocytes. It has now been recognized for some time that the sexual (exogenous) part of the life-cycle of all the Haemamoebidae takes place in an Invertebrate (Insectan) host, and is fundamentally similar to that above described in those cases where it has been followed. In contradistinction to the malarial parasites, this host, in the Avian forms (Haemoproteus and Halteridium),2 is a species of Culex and not of Anopheles; in other words, gamete-formation, conjugation and subsequent sporozoite- formation in these cases will only go on in the former. On the other hand, in the case of the Haemogregarines, it was thought until quite lately that the entire life-history, including conjugation and sporogony, went on in the Vertebrate host; and only in 1902 Hintze described what purported to be the complete life-history of Lankesterella (Drepanidiurrt) ranarum undergone in the frog. This view was rendered obsolete by the work of Siegel and Schaudinn, who demonstrated the occurrence of an alternation of hosts and of generations in the case of Haemogregarina stepanovi, parasitic in a See also:tortoise, and in Karyolysus lacertarum; the Invertebrate hosts, in which, in both cases, the sexual process is undergone, being respectively a leech (Placobdella) and a tick (Ixodes). With this discovery the- main distinction (as supposed) between the Haemosporidia of warm and of cold-blooded Vertebrates vanished.

It was further acknowledged by Schaudinn (under whom Hintze ' This does away with one of the principal reasons on account of which some authorities consider Piroplasma (Leishmania) donovani as quite distinct from other Piroplasmata (see TRYPANOSOMES). 2 It must not be forgotten that one species of Halteridium (H. [Trypanomorpha] noctuae) is said to have well-marked trypaniform phases in its life-cycle; these are preferably considered under Trypanosomes (q.v.), and therefore, to avoid repetition, are only thus alluded to here. Whether H. danilewskyi also becomes trypamform in certain phases, and how far it really agrees with the criteria of a Haemosporidian above postulated, are matters which are not yet definitely known. J. k. 1 which assume the form of the free parasite, as seen in d, e and!. N, Nucleus of the blood - corpuscle. n, Nucleus of the parasite. The outline of the blood-corpuscle is indicated by a thick See also:

black line. had worked) that the latter had been misled by Coccidian cysts and spores, which he took for those of Lankesterella. The gametogony and sporogony of Haemogregarina stepanovi in the leech agree in essential particulars with the process above described.

The micro-gametes are extremely minute, and the sporozoites, which are developed in the salivary glands, where the motile ookinetes finally come to rest, are extremely " spirochaetiform "—the full significance of this latter fact being, perhaps, not appreciated. Christophers recently described some remarkable phases which he regarded as belonging to the cycle of Haemogregarina gerbilli (one of the few Mammalian Haemogregarines known) in a See also:

louse (Haematopinus). In a private communication, however, the author states that he has probably mistaken phases in the development of an ordinary gregarine parasite in the louse for part of the life-cycle of this Haemogregarine. The Mammalian parasite Piro plasma is the one about whose life-history our knowledge is most vague. Besides the typical and generally occurring forms, others have also been observed in the blood, but it is doubtful how far these are to be looked upon as normal; for instance, Bowhill and Le Doux have described, in various species, a phase in which a long, slender pseudopodial-like outgrowth is present, with a swelling at the distal end. It is, moreover, quite uncertain which are the sexual forms, comparable to gametocytes. Doflein regards large pear-shaped forms as such (megagametocytes?), which become spherical when maturing; and Nocard and Motas have figured amoeboid, irregular forms, with the nucleus fragmented and possessing flagella-like processes (possibly microgametes ?). The Invertebrate host is well known to be, in the case of all species, a tick; thus bovine piroplasmosis (P. bigeminum) in See also:America is conveyed by Rhipicephalus annulatus (Boophilus bovis), canine piroplasmosis (P. canis) in See also:South See also:Africa by Haemaphysalis leachi (and perhaps Dermacentor reticulatus), and so on. The manner in which the infection is transmitted by the tick varies greatly. In some cases (e.g. P. bigeminum and P. canis) only the generation subsequent to that which receives the infection (by feeding on an infected ox) can transmit it back again to another ox; in other words, true hereditary infection of the ova in the See also:mother-tick is found to occur. The actual period in the life of the daughter-tick at which it can convey the infection apparently varies.

On the other hand, in the case of See also:

East See also:African See also:coast-fever, Theiler found that hereditary infection does not occur, the same generation transmitting the parasite (P. parvum) at different periods of life. Little is certainly known regarding the phases of the parasite which are passed through in the tick. Lignieres has observed a kind of multiple fission in the stomach, several very minute bodies, consisting mostly of chromatin, being formed, which may serve for endogenous See also:reproduction. See also:Koch has published an account of certain curious forms of P. bigeminum, in which the body is produced into many stiff, ray-like processes, giving the appearance of a See also:star; according to him See also:fusion of such forms takes place, and the resulting zygote becomes rounded, perhaps transitional to the pear-shaped forms. The See also:classification and nomenclature of the Haemosporidia are in a very unsettled condition. For an account of the various systems Classifica- and modifications hitherto adopted, the article of Minchin See also:Eton. (see under SPOxozoA: Bibliography) should be consulted. With the realization that the life-history in the case of the " Haemamoebae " and the Haemogregarines is fundamentally similar in type, the chief reason for grouping them as distinct sub-orders has disappeared. It is most convenient to regard them as separate, but closely allied families, the Plasmodidae (" Haemamoebidae ") and the Haemogregarinidae. The Piroplasmata, on the other hand, constitute another See also:family, which is better placed in a distinct section or sub-order. . In addition there are, as already noted, two or three genera whose systematic position must be considered as quite uncertain. One is the well-known Halteridium of Labbe, parasitic in various birds; the type-species is H. danilewskyi (Gr. and Fel.).

Another is the much-debated parasite of See also:

white blood-corpuscles (leucocytes), originally described in birds by Danilewsky under the name of Leucocytozoon, a form of which has been recently observed in Mammals. In conclusion, the chief members of the above-mentioned families may be enumerated. Fam. Plasmodidae (" Haemamoebidae "). Genus Laverania, Gr. and Fel. (syn. Haemamoenas, Ross), for L. malariae, Gr. and Fel. (synn. L. s. Plasmodium, s. " Haemamoeba," &c., praecox s. immaculatum, &c.), the parasite of pernicious malaria. Genus Plasmodium, See also:March. and Celli (syn.

" Haemamoeba") for P. vivax and P. malariae, the tertian and quartan parasite, respectively. There is also a form known in apes, P. kochi. Genus Haemoproteus, Kruse (syn. Proteosoma), for H. danilewskyi (syn. Proteosoria grassi, Plasmodium praecox, &c.), parasitic in numerous birds. Recently, another form has been described, from See also:

reptiles, which Castellani and Willey have termed Haemocystidium simondi. Remarks.—The distinguishing characters of the malarial parasiteshave been mentioned above. Some authorities would include Laverania in the genus Plasmodium, as differing only specifically from the other two forms. It has, moreover, been suggested by Sergent that all three are merely different phases of the same parasite, predominating at different seasons; this See also:idea cannot be regarded, however, as in any way proved so far. From what is known of the schizont, with numerous merozoites. f, Gametocyte. N, Nucleus of blood-corpuscle. n, Nucleus of parasite.

p, Pigment. mz, Merozoites. r.p, Residual See also:

protoplasm. See also:morphology and mode of manifestation of these forms, the differences between Laverania and the two species of Plasmodium are consider-ably more pronounced than those between P. vivax and P. malariae; if the latter are to be considered as distinct species, the first-named is probably generically distinct. Luhe, it may be noted, in his recent comprehensive account of the Haematozoa, also takes this view. Lastly, whatever be the correct See also:solution of the above problem, there is certainly not sufficient See also:justification for including the Avian genus Haemoproteus, as also only a species of Plasmodium, which is done by some. Its different Vertebrate habitat, and also the fact that its Insectan definitive host is Culex and not Anopheles, differentiate it sharply from Laverania and Plasmodium. Fam. Haemogregarinidae.—The different genera are characterized a, Blood-corpuscle with young trophozoite. b, Older trophozoite. c, Full-grown trophozoite, ready to leave the corpuscle. d and e, Trophozoites free in the blood-plasma, showing changes of form.

f-i, Trophozoites, still within the blood-corpuscle (not drawn), showing the structure of the nucleus, the coarse chromatoid granules in the protoplasm and the manner in chiefly by their size relative to the blood-corpuscles, and their disposition in the latter. Here, again, it has been suggested to unite the various types all in one genus, Haemogregarina, but this seems at least premature when it is remembered how little is known in most cases of the life-cycle, which may prove to exhibit important divergences. Genus Haemogregarina, Danilewsky (syn. Danilewskya, Labbe). f. g h. From Lankester's Treatise on Zoology. d. From Lankester's Treatise on Zoology. a, Young trophozoite in a blood-corpuscle. b and c, Older trophozoite. d and e, Sporulation. d, Precocious sporulation with few merozoites.

e, Sporulation of a full-grown which the parasite grows into the U-shaped Haemogregarine without increase of body-See also:

mass. Commencement of sporulation; the nucleus has divided into eight nuclei, and the body of the parasite is beginning to See also:divide up into as many merozoites within a blood-corpuscle. N, Nucleus of the blood-corpuscle. n, Nucleus of the parasite. j, The body of the parasite exceeds the blood-corpuscle in length, when adult, and is See also:bent upon itself, like a U. A very great number of species are known, mostly from reptiles and fishes; among them may be mentioned H. stepanovi (fig. 6), from Emys and Cistudo, whose sexual-cycle in a leech has been worked out by Siegel (see above), H. delagei, from See also:Raja, H. bigemina, from blennies, and H. simondi, from soles. Recently one or two Mammalian forms have been observed, H. gerbilli, from an See also:Indian See also:rat (Gerbillus), and H. jaculi, from the See also:jerboa. Genus Lankesterella, Labbe (syn. Drepanidium, Lankester). The parasite is not more than three-quarters the length of the corpuscle. L. ranarum from Rana is the type-species; another, recently described by Fantham, is L. tritonis, from the See also:newt.

Genus Karyolysus, Labbe. The parasite does not exceed the corpuscle in length ; the forms included in this genus, moreover, d' From Lankester's Treatise on Zoology. although not actually intranuclear, have a marked karyolytic and disintegrating See also:

action upon the nucleus of the corpuscle. The type-species is the well-known K. lacertarum, of lizards; another is K. (Haemogregarina) viperini, from Tropidonotus. In the section of the Piroplasmata there is only the genus Piro-plasma, See also:Patton (synn. Babesia, Starcovici, Pyrosoma, See also:Smith and Kilborne), the principal species of which are as follows: P. bigeminum, the cause of Texas cattle-fever, tick-fever (Rinder-malaria) of South Africa, and P. bovis, causing haemoglobinuria of cattle in Southern See also:Europe; there is some uncertainty as to whether these two are really distinct; P. canis, P. ovis and P. equi associated, respectively, with those animals. Lately, a very small form, P. parvum, has been described by Theiler in See also:Rhodesia, which. causes East-African coast-fever; and another, P. muris, has been observed in white rats by Fantham. Haemogregarine of Mammals," J. Trop. Med. 8, p.

241, 8 See also:

figs. (1905); C. A. See also:Bentley, " Leucocytozoan of the See also:Dog," B.M.J. (1905), I, pp. 988 and Io78; N. Berestneff, " Uber einen neuen Blutparasiten der indischen Frosche," See also:Arch. Protistenk. 2, p. 343, pl. 8 (1903); " Uber das Leucocytozoan ' danilewskyi," op. cit. 3, p.

376, pl. 15 (1904); A. See also:

Billet, " Contribution a 1'atude du paludisme et de son hematozoaire en Algarie," See also:Ann. Inst. See also:Pasteur, 16, p. 186 (1902) ; (Notes on various Haemogregarines), C. R. See also:Soc. Biol. 56, pp. 482, 484, 607 and 741 (1904); C. Borner, " Untersuchungen Ober Hamosporidien," Zeiischr. wiss.

Zool. 69, P. 398, 1 pl. (1901); T. Bowhill, " Equine piroplasmosis," &c., J. Hyg. 5, p. 7, pls. 1-3 (1905) ; Bowhill and C. le Doux, " Contribution to the Study of Piroplasmosis canis,' " op. cit. 4, p. 217, pl. 11 (1904) ; E.

Brumpt and C. Lebailly, " Description de quelques nouvelles especes de trypanosomes et d'hamogragarines," &c., C. R. Ac. Sci. 139, p. 613 (1904) ; A. Castellani and A. Willey, " Observations on the Haematozoa of Vertebrates in See also:

Ceylon," Spolia Zeylan. 2, p. 78, I pl. (1904), and Q.

J. Mier. Sci. 49, p. 383, pl. 24 (1905); S. R. Christophers, Haemogregarina gerbilli," Sci. Mem. See also:

India, 18, 15 pp., I pl. (1905) ; H. B.

Fantham, 'Lankesterella tritonis, n. sp., " &c., Zool. Anz. 29, p. 257, 17 figs. (1905) ; " Piroplasma muris," &c., Q. J. Mice. Sci. 50, p. 493, pl. 28 (1906); C. See also:

Graham-Smith, " A new Form of Parasite found in the Red Blood-Corpuscles of Moles," J.

Hyg. 5, p. 453, pls. 13 and 14 (1905) ; R. Hintze, " Lebensweise and Entwickelung von Lankesterella minima," Zool. Jahrb. Anat. 15, p. 693, pl. 36 (1902); S. See also:

James, " On a Parasite found in the White Blood-Corpuscles of Dogs," Sci. Mem.

India, 14, 12 pp. I pl. (1905); R. Koch, Vorlaufige Mitteilungen fiber die Ergebnisse eingr Forschungsreise nach Ostafrika," See also:

Deutsch. med, Wochenschr., 1905, p. 1865, 24 figs.; A. Labbe, " Recherches sur See also:les parasites endoglobulaires du sang See also:des vertebras," Arch. See also:tool. exp. (3) ii• p. 55, to pls. (1894) ; A. Laveran, " Sur quelques hemogregarines des ophidiens," C. R. Ac.

Sci. 135, p. 1036, 13 figs. (1902) ; " Sur une Haemamoeba d'une mesange (Parus See also:

major)," C. R. Soc. Biol. S4, p. 1121, 10 figs. (1902) ; " Sur la piroplasmose bovine bacilliforme," C. R. Ac.

Sci. 138, p. 648, 18 figs. (1903); " Contribution a 1'6tude de Haemamoeba ziemanni," C. R. Soc. Biol. 55, p. 620, 7 figs. (1903) ;" Sur une h6mogregarine des gerboises,'' C. R. Ac.

Sci. 141, p. 295, 9 figs. (1905) ; (On different Haemogregarines) C. R. Soc. Biol. 59, pp. 175, 176, with figs. (1905) ; " Haemocytozoa. Essai de classification," See also:

Bull. Inst.

Pasteur, 3, p. 809 (1905); Laveran and F. Mesnil, " Sur les hematozoaires des poissons marins," C. R. Ac. Sci. 135, p. 567 (1902); " Sur quelques protozoaires parasites d'une tortue d'Asie," i.c. p. 609, 14 figs. (1902); Laveran and Negre, " Sur un protozoaire parasite de Hyalomma aegyptium," C. R. Soc.

Biol. 58, p. 964, 6 figs. (1905); (for various earlier papers by these authors, reference should be made to the C. R. Ac. Sci. and C. R. Soc. Biol. for previous years) ; C. Lebailly (On Piscine Haemogregarines) C. R.

Ac. S'ci. 139, p. 576 (1904), and C. R. Soc. Biol. 59, p. 304 (1905) ; J. Lignieres, " Sur la ' Tristeza,' " Ann. Inst. Pasteur, 15, p.

121, pl. 6 (1901) ; " La Piroplasmose bovine; nouvelles recherches," &c., Arch. parasit. 7, p. 398, pl. 4 (1903); M. Liihe, "Die See also:

im Blute schmarotzenden Protozoen," in Mense's Handbuch der Tropenkrankheiten (See also:Leipzig, 1906), 3, 1; F. Marceau, " Note sur le Karyolysus lacertarum," Arch. parasitol. 4, p. 135, 46 figs. (1901); W. MacCallum, " On the Haematozoan Infection of Birds," J. Exp.

Med. 3, p. 117, pl. 12 (1898); G. Mauser, " Die Malaria perniciosa," Centrbl. Bakter. (i) 32, Orig. p. 695, 3 pls. (1902); C. Nicolle (On various Reptilian Haemogregarines), C. R. Soc.

Biol. 56, pp. 3yO, 608 and 912, with figs. (1904) ; Nicolle and C. See also:

Comte, " Sur le role de Hyalomma dans l'infection hamogragarinienne," op. cit. 58, p. 1045 (1905); Norcard and Motas, " Contribution a 1'6tude de la piroplasmose canine," Ann. Inst. Pasteur, 16, p. 256, pls. 5 and 6 (1902); G. See also:Nuttall and G.

Graham-Smith, " Canine piroplasmosis," J. See also:

Hygiene, p. 237, pl. 9 (1905) ; F. Schaudinn, " Der Generationswechsel der Coccidien and Hamosporidien," Zool. Centrbl. 6, p. 675 (1899); " Studien fiber krankheitserregende Protozoen—II. Plasmodium vivax," Arb. Kais. Gesundheitsamte, 19, p. 169, pls.

4-6 (1902); E. and E. Sergent (On different Haemogregarines), C. R. Soc. Biol. 56, pp. 130, 132 (1904), op. Cit. 58, pp. 56, 57, 670 (1905); Siegel, " Die geschlechtliche Entwickelung von Haemogregarina,' &c., Arch. Protistenk. 2, p.

339, 7 figs. (1903); P. L. Simond, " Contribution a 1'atude des hematozoaires endoglobulaires des reptiles," Ann. Inst. Pasteur, 15, p. 319, I pl. (1901); T. Smith and F. Kilborne, " Investigations into the Nature, See also:

Causation and Prevention of Texas Cattle Fever," See also:Rep. See also:Bureau Animal See also:Industry, U.S.A., 9 and To, p. 177, pls.

(1893) ; A. Theiler, " The Piroplasma bigeminum of the Immune Ox," J. See also:

Army Med. Corps, 3, pp. 469, 599, I pl. (1904) ; J. See also:Vassal, " Sur une hematozoaire endoglobulaire nouveau d'un mammifere," Ann. Inst. Pasteur, 19, p. 224, pl. 10 (1905) ; L. B.

Wilson and W. Chowning, " Studies in Piroplasmosis hominis," J. Infect. Diseases, 1, p. 31, 2 pis. (1904). (H. M.

End of Article: HAEMOSPORIDIA

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