PARASITES 353 



Christiansen (25)) connect the blepharoplasts with the posterior tip of the 

 organism where they give rise to the pair of caudal flagella. A fourth pair 

 of flagella arises ventrally from the axostyles just posterior to the nuclei. 

 Two deeply staining bodies lie dorsal to the axostyles. Both binary and 

 multiple fission take place in the nonencysted stage (19). 



Cysts form and are passed out with the feces, and undoubtedly infection 

 occurs by the ingestion of the cysts in contaminated food and water. 



Slight infections are apparently not greatly harmful to laboratory mice, 

 although more severe infections cause enteritis. Kofoid and Christiansen 

 (25) have noted that in mice the organism gives rise to a readily recognizable 

 enteritis which appears as a chronic condition in young mice. 



Haemoflagellates 



Trypanosoma duttoni thiroux. — The trypanosome described as occur- 

 ring naturally in the blood plasma of the mouse is T. duttoni. 



As is typical of trypanosomes this form is a spindle-shaped organism. 

 The fiagellum arises near the posterior end of the body, passes anteriorly, 

 is connected to the body by an undulating membrane, and extends beyond 

 the anterior end. This species of trypanosome is quite slender, measuring 

 about 25 /x in length, and the fiagellum is long. Anatomically it cannot be 

 distinguished from the more familiar T. lewisi found in the rat. 



Apparently the life cycles of the two forms are also much the same. It 

 is well known that T. lewisi employs the rat flea as its intermediate host, 

 the rat becoming infected by swallowing the feces of the infected flea; and 

 Brumpt (6) has shown that the swallow flea could be made to act as the 

 intermediate host for T. duttoni. He demonstrated a cycle development in 

 the swallow flea and was able to infect mice by feeding them feces of the 

 infected fleas. While this was obviously not the natural intermediate host, 

 it does suggest that fleas occurring on mice may well act as the vectors. 



Trypanosoma duttoni like T. lewisi is generally considered to be non- 

 pathogenic, but obviously it can occasionally cause fatal infection. Roud- 

 sky (32), by rapid inoculations from rat to rat of the whole blood of an 

 animal when the trypanosomes were at the multiplication phase, was able 

 to raise the virulence of T. lewisi until it was not only transmissible to 

 the mouse but was definitely pathogenic for the mouse as shown by the 

 hepatic and splenic lesions caused, and the infection proved to be transmissi- 

 ble from mouse to mouse. Later (t,^) he was able by a similar procedure 

 to increase the virulence of T. duttoni until it was infective when inoculated 

 into the rat. 



