TRYPANOSOMES OF RODENTS 475 



uiulergo clianges comparable to those seen in artificial culture in blood 

 media in the stomach of bed bugs and other arthropods, where a compara- 

 tively large quantity of blood is taken in and only slowly digested. This 

 condition must not be mistaken for true infection. It has been a constant 

 source of errors in experimental work with flagellates and biting arthropods. 

 In many cases it may be difficult to decide between cultural developments 

 and true infections, but in the latter the parasites tend to persist for long 

 periods in spite of constant feeding, whereas, in the former, a second feed 

 of blood often causes the flagellates to vanish. The experiments of 

 Patton, La Frenais, and Rao (1921), referred to on p. 355, are of interest 

 in this connection. 



(a) Other Trypanosomes of Rodents, 



The trypanosomes of rodents include the majority of forms known 

 to occur in small mammals. The best known is T. lewisi of tlie rat, 

 which has been dealt with above in some detail, and all the trypanosomes 

 of this group resemble it closely. Species have, however, been created on 

 slight differences in size, the failure of rats to become infected after 

 inoculation, and the immunity of the hosts to infection with T. lewisi. 

 In the few cases where it has been possible to study the complete develop- 

 ment in the vertebrate, the resemblance to T. lewisi is very marked. The 

 course of development in fleas in those cases which have been investigated 

 is also identical with that of T. lewisi. It is possible that most, if not all, 

 of these forms represent races of T. lewisi which have become adapted to 

 particular hosts. It is evidently impossible to place reliance on differential 

 characters which are based on slight morphological variations, especially 

 when it is remembered that in the case of T. lewisi what were merely 

 difi'erent stages of development of this trypanosome have been given 

 special specific names. 



Trypanosoma duttoni Thiroux, 1900. — This is a trypanosome which 

 occurs in mice {Mus morio and M. tnusculus) in various parts of the world. 

 According to Laveran and Mesnil (1912), in dimensions and method of 

 multiplication in the mouse it closely resembles T. lewisi (Fig. 201, 9). 

 Though easily inoculable from mouse to mouse, rats and guinea-pigs are 

 not infected. Roudsky (1912), however, was able to increase its virulence 

 till it was inoculable to rats, just as he raised the virulence of T. lewisi, 

 as shown above, till mice became susceptible. Brumpt (1913) w^as able 

 to demonstrate that T. duttoni had a cycle of development in the swallow 

 flea, Ceratophyllus hirudinis, like that of T. lewisi. In the faeces of the 

 fleas were found the small infective trypanosomes, and seven mice which 

 were fed with the faeces became infected. The swallow flea can hardly 

 be the natural host of the mouse trypanosome, yet in this flea its 



