468 



FAMILY: TRYPANOSOMIDiE 



intravenously into healthy rats, no multiplication of the trypanosomes 

 occurs, and no infection results, whereas, if the same experiment is con- 

 ducted with the serum of a normal rat, the trypanosomes multiply and 

 infection results in the usual manner. Coventry (1925) could not detect 

 this substance in the blood of rats before the fifth day of an infection, 

 though it is undoubtedly present, as reproduction is declining before this. 

 There is a rapid increase in the quantity present in the blood between the 

 fifth and sixth days, and a more gradual one up to the thirty-fifth day, 

 after which it decreases up to the time when the infection ends. 



Culture. — T. leivisi is readily cultivated in blood-agar media, and 

 can be maintained for indefinite periods by subculture. In these cultures, 

 the trypanosome forms disappear till every type of organism between 



leishmania and crithidia forms 

 are met with, and large clus- 

 ters of flagellates of all kinds 

 are formed in which the organ- 

 isms are arranged with their 

 flagella directed inwards to- 

 wards the centre of the mass. 

 Delanoe (1911) showed that 

 in old cultures trypanosome 

 forms tend to reappear. They 

 differ in structure from those 

 originally introduced, and bear 

 a striking resemblance to the 

 infective metacyclic trypano- 

 somes which are produced in 

 the rectum of fleas. This 

 observation lends support to the view that the type of development 

 which occurs in the culture tube is an imitation of the invertebrate cycle 

 of the trypanosome. 



The cultural form of T. lewisi will infect rats, though after long 

 maintenance by subculture its power of doing so becomes diminished. 



Pathology. — In its normal condition T. lewisi is not pathogenic to 

 rats, which naturally recover from their infections. In accordance with 

 this, practically no change is produced in the organs. In the strains of 

 heightened virulence studied by Roudsky (1910-1911) degenerative 

 changes with enlargement of the organ and lymphoid infiltrations occur 

 in the liver and spleen. 



Transmission." — That T. leivisi was transmissible from rat to rat by 

 fleas was first proved by Eabinowitsch and Kempner (1899), who infected 



Fig. 198. — Ceratophyllns fasciatus, the Trans- 

 mitter OF Trypanosoma lewisi ( x 20). 



(Original.) 



