THE PATHOGENIC HEMOSPORIDIA 273 



(Ross, 1905), in goats, horses, and asses (Ziemann), and in man 

 (Wilson and Chowning, 1901 ; Anderson, 1903). 



In all cases the medium of transmission, where known, is some 

 species of tick, and with their discovery of this important function of 

 tracheates. Smith and Kilborne ('93) opened up a new era in the his- 

 tory of preventive medicine, a discovery followed by the brilliant work 

 of Bruce with trypanosomes and flies; of Ross and Grassi with malaria 

 organisms and mosquitoes; and of a host of other investigators upon 

 blood parasites in all kinds of animals. 



Structural Characteristics. — Unlike Herpetomonas donovani an endo- 

 thelial parasite, or unlike the serum-dwelling forms of flagellates gen- 

 erally, the various species of babesia are intracorpuscular parasites, 

 although at periods they may become free in the serum. The general 

 form is spherical or pear-like (whence the names piroplasma and piro- 

 plasmosis), the size varying from 0.5 fx (Smith and Kilborne for B. bovis) 

 to 5 fi (occasionally in B. canis, according to Nuttall and Graham- 

 Smith). As a rule, they are single in the blood corpuscles in peripheral 

 blood (50 to 76 per cent., according to Graham-Smith, in dogs with 

 B. canis), although double infection, arising usually by division of the 

 parasite, occurs in from 20 to 30 per cent. Such double ones were 

 regarded as characteristic by Smith and Kilborne, who suggested the 

 name "bigemina" for the organism of Texas fever (^Babesia bovis). 



The parasite of dogs, Babesia canis, has been more thoroughly 

 studied than any other form, and furnishes a good object for general 

 description. It has been monographed by Nuttall and Graham- 

 Smith ('05-'07), by Kinoshita ('07), by Bowhill and Le Doux ('04), 

 by Christophers ('07), and by Breinl and Hindle ('08), so that, 

 although the various observers are not always in agreement, nor 

 the life history in any case complete, there is a good basis of facts 

 for others to work on. 



According to all observers, the living parasite is very active, throwing 

 out processes of pseudopodial nature at various points of the periphery, 

 and with such vigor " as sometimes to move the corpuscle in which the 

 parasite is situated" (Christophers). Sometimes these protoplasmic 

 processes are drawn out into long filaments resembling flagella (Fig. 

 107), while crescents, ring forms, triangles, etc., are forms assumed at 

 one time or another, the greatest activity being shown during the 

 febrile state (Nocard and Motas). 



The nucleus of the cell, like that of plasmodium, is of indefinite 

 shape, consisting of chromatin granules arranged in rod, ring, or semi- 

 circular form, the size and form of the aggregate giving an indication 

 of the developmental period (Kinoshita). The nucleus is usually 

 excentric in position, becoming flattened at times against the periphery 

 of the cell, but in free forms it usually lies in the centre of the para- 

 site (Christophers). 

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