SPOROZOA 



763 



the mature cyst, these collect in large numbers in the salivary glands 

 and ducts. 



The life history of the parasite is seen to be like that of proteosoma 

 and malaria, except that the asexual or schizogenous cycle appears to 

 be lacking. 



Proteosoma (plasmodium) praecox. This parasite is a typical rep- 

 resentative of the sporozoa, and is interesting historically, since it was 

 the one with which Ross worked in 1898, when he first demonstrated 

 the part played by the 

 mosquito in "bird ma- 

 laria.' 7 



Grassi and Feletti de- 

 scribed the parasite iri 

 1890 under the name of 



hemamcba precox. It is 



A B C D 



FIG. 181. PROTEOSOMA PRAECOX IN BLOOD OF 

 FIELD LARK. A, Young parasite in blood cell; 

 B, Half-grown parasite which has pushed aside 

 nucleus of blood cell; C, Parasite with clump 

 of pigment and many nuclei; D, Division into 

 many merozoites. (After Doflein and Wasie- 

 lewski. MacNeal, "Pathogenic Microorgan- 

 isms," published by P. Blakiston's Sons & Co.) 



widely distributed geo- 

 graphically, and is com- 

 mon in the blood of small 

 birds, sparrows, robins and 

 larks. It can be propa- 

 gated in the laboratory in 

 the blood of canaries with- 

 out great difficulty; spar- 

 rows, however, do not long survive in captivity unless kept in round 

 glass jars, where they cannot injure themselves by dashing against 

 the walls. The blood for examination is obtained from the cephalic 

 wing vein, close to the body, which is nicked with a razor, and the 

 blood taken up in a capillary glass tube containing a little citrate 

 solution. To inoculate a new bird, it is sufficient to inject a small 

 quantity of citrated blood from an infected canary into the breast 

 muscles of the new bird, transferring to a new host at intervals of 

 a month or less. Because it is not difficult to keep on hand, this organ- 

 ism may be used for class study in localities where malarial cases are 

 infrequent. There is no apparent reason for placing -it in a different 

 genus from the malarial parasites. 



The entire asexual cycle, schizogony, may be studied in the periph- 

 eral circulation, as in quartan malarial fever. 



In nature it is transmitted by both culex and stegomyia (Aedes 

 calopus), and its development is briefly as follows: The bird is inocu- 

 lated by the mosquito with spindle-shaped young forms known as 



