474 FAMILY: TRYPANOSOMID.E 



an opportunity of feeding on rats. For instance, Brunipt (1913) showed 

 that the swallow flea, C. hinulinis, might serve as a host for T. Jewisi, 

 and that the faeces of the fleas were infective to rats in the usual manner, 

 while Noller {\^12d) showed that the development could take place in 

 Ctenopsylla musculi. 



It is highly probable tliat in nature infection may take place by rats 

 actually devouring the infected fleas themselves. 



From the above description it will be seen that the development in 

 the flea consists of an intracellular multiplication phase in the stomach, 

 followed by the transformation of the trypanosomes into crithidia forms 

 and their migration to tlie rectum, where the attached phase results. 

 Eventually, after the expiry of six days from the time of feeding, small 

 metacyclic trypanosomes are voided in the faeces and ingested by the 

 rats. It is important to note that at no stage was a sexual process 

 encountered. Yamasaki (1924), who claims that the dog flea can transmit 

 the trypanosome by its proboscis, also states that the intracellular stage 

 is not essential to complete development in the flea. 



Possible Transmission by Other Arthropods. — In addition to the experi- 

 mental work with fleas, a good deal of attention has been paid to 

 the rat louse, Hcematopinus spinulosus. Prowazek (1905) described a 

 developmental process, including syngamy, in the louse, leading to infec- 

 tion, not only of the gut, but also the body cavity fluid. The trypano- 

 somes were supposed to be inoculated to the rat by the bite of the louse. 

 Subsequent observation has not confirmed the developmental cycle, 

 though it has been definitely shown by McNeal (1904), Nuttall (1909), and 

 Baldrey (1909) that infection can be conveyed to rats by transferring lice 

 from infected animals. Noller (1914) studied the question of louse 

 transmission, and was unable to find any evidence in favour of Prowazek's 

 sexual phase, nor of the invasion of the body cavity fluid or biting organs. 

 According to him, T. lewisi undergoes changes in the intestine of the 

 louse, which are comparable to the culture of the trypanosome in artificial 

 media. No established infection is produced in them as in the case of the 

 flea, which, once infected, remains so for the rest of its life owing to con- 

 tinued m\dtiplication of the attached forms in the rectum. The faeces of 

 lice which have ingested infected blood will produce infection if eaten by 

 the rat, as also will the louse itself, and Noller thinks that in nature the 

 louse may convey the trypanosome in a mechanical manner by being 

 devoured while it still has trypanosomes within it, though as a vector it is 

 of little importance compared with fleas. Several observers have shown 

 that rats can be infected by feeding them with the blood or organs of 

 infected rats. 



It has been shown by the writer (19r2c) and otliers that T. lewisi will 



