TRYPANOSOMA MELOPHAGIUM 505 



is usually present in small numbers in the blood of infected sheep, and, 

 as in the case of T. theileri, its presence is best detected, as first shown 

 by Behn (1911), by the use of thick films or, as N5ller (1920c) demon- 

 strated, by abstracting blood from a vein and diluting it in culture tubes 

 under sterile conditions with an equal quantity of bouillon. The mixture 

 is incubated at 30° C. for a week or more, after which time the scanty 

 trypanosomes w^ll have multiplied sufficiently to be readily detected. 

 By the culture method Hoare was able to demonstrate that the sheep in 

 a ked-infested flock were infected Lo the extent of 80 per cent. In lambs 

 which were experimentally infected by feeding them with the hind-gut 

 of keds, the trypanosomes are for a short time sufficiently numerous to be 

 detected in the blood by the examination of a few wet films. The infection, 

 however, subsides in the course of one to three months, and if the animals 

 are kept free from keds it will disappear entirely. The sheep, however, 

 can be readily reinfected, and it seems probable that there is only a very 

 slight degree of immunity, and that flocks of sheep are kept infected by 

 constant reinfection. The trypanosome appears to have no harmful effect 

 on the sheep. 



The trypanosome in the blood of the sheep is of large size, like T. thei- 

 leri (Fig. 215). It is from 50 to 60 microns in length, and the portion of 

 the body behind the kinetoplast is pointed and represents about one- 

 third the length of the entire body. The nucleus is central in position, 

 and the kinetoplast is a short distance behind it and about 9-6 microns 

 from the posterior end. There is a short free flagellum about 5-6 microns 

 in length. No multiplication forms have been seen in the blood. 



The early stages of development in the ked have not been followed, 

 but these insects are practically invariably infected when taken oft" sheep. 

 The predominating type is a crithidia which appears to be confined to the 

 Stomach (Fig. 215, 2-3). It multiplies rapidly by longitudinal fission, and 

 becomes attached in large numbers to the wall of the hind-gut, especially 

 round the pyloric opening of the stomach. In this attached condition 

 many of the crithidia forms by repeated divisions unassociated with growth 

 become smaller forms, which by migration backwards of the kinetoplast 

 to the posterior extremity of the body are transferred into short stumpy 

 metacyclic trypanosomes (Fig. 215, 4-5). The latter are presumably 

 those which lead to infection of the sheep. They resemble in many respects 

 the small metacyclic trypanosomes of T. lewisi. 



Cultures of the trypanosome, whether commenced from the blood of 

 sheep or from the intestine of the ked, can be maintained at 30° C. in 

 Noller's medium, which consists of N.N.N, medium to which glucose has 

 been added. In the cultures from the sheep's blood large trypanosomes 

 at first occur, but these quickly become crithidia forms like those in cultures 



