176 THE ANIMAL PARASITES OF MAN 



the expense of the parent form until they become two pear-shaped 

 parasites joined at their pointed ends. The connecting strand shrinks 

 and the two daughter forms separate (fig. 91, 10 14). The pyriform 

 parasites after having exhausted the blood corpuscle escape from it 

 (fig. 91, 15), and seek out fresh host corpuscles, entering by the rounded, 

 blunt end (fig. 91, i). It is the pyriform phase of the parasite which 

 penetrates red blood corpuscles, not rounded forms, which die if set 

 free. The pyriform parasite, however, becomes rounded (fig. 91, 2, 3), 

 soon after its entry into a fresh host cell. This interesting mode of 

 division by gemmation and chromatin forking has been made dia- 

 gnostic of the genus Babesia by Nuttall. 1 Rounded forms of Babesia 

 divide by binary fission, and this direct method can also be adopted 

 by the other forms of Babesia. 



The distribution of the chromatin in the pear-shaped Babesia, as seen in B. cants 

 and B. bovis, is interesting. The main nuclear body consists of a karyosome 

 surrounded by a clear area. There is also a loose (chromidial) mass of chromatin 

 representing the remains of the chromatin forks seen during the formation of the 

 parasite as a daughter form by gemmation. Occasionally there is a small dot or 

 point, the so-called "blepharoplast" of Schaudinn and Liihe. This minute dot is 

 not a flagellate blepharoplast, for there is no flagellate stage in the life-history of 

 Babesia. These nuclear phenomena have been described by Nuttall and Graham- 

 Smith and Christophers (iQoy) 2 for B. canis, by Fantham (i9O7) 3 for B. bovis, and 

 by Thomson and Fantham (1913) from glucose-blood cultures of B. cants. 



Babesia are tick borne, as was first shown by Smith and Kilborne 

 (1893). The developmental cycle in the tickis in completely known. 

 The best accounts are those of Christophers (i9O7) 4 for B. canis and 

 Koch (1906) for B. bovis, and these accounts are supplementary. 

 The principal stages, so far as known, may be summarized thus : 



(1) The piroplasms taken by the tick in feeding on blood pass into the tick's 

 stomach. The pyriform parasites, which alone are capable of further development, 

 are set free from the blood corpuscles. In about twelve to eighteen hours they 

 become amoeboid, sending out long, stiff, slender, pointed pseudopodia. The 

 nucleus of each parasite divides unequally into two. Similar forms have been 

 obtained in cultures. These stellate forms may be gametes, and according to Koch 

 fuse in pairs. 



(2) A spherical stage follows, possibly representing the zygote. This grows, and 

 a uninucleate globular mass results. This form is found in large numbers on the 

 third day, according to the observations of Koch. 



(3) A club-shaped organism is next formed. This may represent an ookinete 

 stage. The club-shaped bodies are motile and gregarine-like, and are about four 

 times the size of the blood forms. These club-shaped bodies and subsequent stages 

 were described by Christophers in the development of B. canis in the dog-tick, 

 Rhipicephalus sanguineus. 



1 " Piroplasmosis," Herter Lectures, Parasitology, vi, p, 302. 



2 Set. Me >ns. Govt. India, No. 29. 



3 Quart. Journ. Microsc. Set., li, p. 297. 



4 Sci. Mcms. Goi-t. India, No. 29. 



