64 ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



the gametocyte has a very markedly crescentic form. These species of 

 Proteosoma and Haemoproteus are of historical interest for as already 

 indicated it was in them that the process of syngamy was first observed 

 (Haemoproteus} and the details of the sporogony cycle first worked out 

 (Proteosoma of Indian Birds). 



A group of parasites of great practical importance are those which 

 are grouped under the generic name Babesia or Piroplasma (Fig. 26). 

 These are small amoeboid parasites of red blood-corpuscles, commonly 

 rounded or oval in form. Within the corpuscle they reproduce by fission 

 so that commonly two occur together within a single corpuscle and 

 sometimes four or eight. Whether or not a sexual or sporogony cycle 

 occurs and whether or not there is an actively swimming flagellate 

 phase are questions not as yet satisfactorily answered. 



The best-known species of Babesia (B. bovis or B. bigeminum) is that 

 which causes the very destructive disease of Caltle known by such names 

 as Texas Fever North America, Tristeza 

 Spanish America, Redwater Fever (i.e. 

 Haemoglobinuria) Australia. The life- 

 history of this parasite was first blocked 

 out by Smith and Kilborne (1893) in North 

 FlG - 26 - America. 



TWO red blood- The d i sease i s endemic in various regions 



corpuscles of a mammal infected 



with Babesia. in the corpuscle in the Southern States and Mexico. Cattle 

 on the left the parasite has under- dri northwards during the warm season 



gone fission into two. 



from these infected areas were found to 



infect pastures through which they were driven. Two important 

 peculiarities were observed in this infection, (i) The herds of cattle 

 were found gradually to lose their power of infecting new pastures as 

 they were driven further and further northwards. (2) It was found that 

 a newly infected pasture did not communicate the disease until at 

 least 30 days had elapsed since the passage of the infective herd. Both 

 of these puzzling peculiarities were explained when the mode of trans- 

 mission of the parasite was worked out. 



Transmission is carried out through the agency of intermediate hosts 

 Ticks (see p. 257) of the genus Rhipicephalus or Boophilus, the precise 

 species being different in different parts of the world. 



If, and only if, infected blood is taken in by an adult female Tick 

 certain pear-shaped individuals of the Babesia leave the blood-corpuscles, 

 put out long slender radiating pseudopodia, and wander away through 

 the tissues of the Tick's body, some of them reaching the ovary and 

 creeping into the substance of the eggs which become thus infected. 



