530 FAMILY: TRYPANOSOMIDiE 



As already remarked, trypanosomes occur in the cerebro-spinal fluid. 

 Here they may be found in the later stages of the disease, and are peculiar 

 in that they exhibit a marked want of uniformity in size and shape- 

 Curious rounded, stumpy, or pear-shaped forms are often encountered. 

 These are to be regarded as abnormal or involution forms, and are of no 

 special significance in the life-history of the trypanosome. 



Susceptibility of Animals. — It is possible to inoculate T. gaynhiense 

 into all the ordinary laboratory animals. Monkeys are readily infected, 

 but baboons (Cynocephalus) are refractory. Those of the genera Macacus, 

 Cyno7nolgus, and Cercopithecus (especially C. ruber) are very susceptible. 

 The smaller animals such as rats, mice, guinea-pigs, and rabbits are not so 

 readily infected as monkeys when the inoculations are made directly from 

 man. After a strain has passed through a monkey, it becomes more virulent 

 for the smaller animals. The dog and the cat are susceptible, as also 

 goats, sheep, horses, and cattle. Fowls are inoculated with difficulty. The 

 course of infection in these animals varies considerably. The virulence 

 of any particular strain increases with passage from animal to animal till 

 it causes death in two to three weeks in rats and guinea-pigs, and even in 

 monkeys. The first passage from man may, in small animals, give rise 

 to an infection lasting several months, or even a year or more, during which 

 time trypanosomes are with difficulty discovered in the blood. In the 

 larger domestic animals the infection is of a mild and chronic type, 

 trypanosomes often being demonstrable only by inoculation of their blood 

 into more susceptible animals. 



Animal inoculations are of service as an aid to diagnosis. One or two 

 cubic centimetres of blood from a man may be inoculated intraperitoneally 

 into a rat or guinea-pig, or larger quantities into a monkey. It must be 

 remembered that a failure to produce infection does not prove that 

 trypanosomes are absent. In the writer's experience, inoculation 

 of fairly large quantities of blood known to contain trypanosomes 

 into rats has not infrequently failed to give rise to any recognizable 

 infection. 



Culture. — In the usual blood media, as, for instance, N.N.N, medium, 

 which answers well for many flagellates of this group, T. gamhiense may 

 survive for a fortnight or more, and show changes of structure to the 

 crithidia type, but it does not multiply to any extent, so that the main- 

 tenance of a culture by sub-inoculation of fresh tubes does not succeed, 

 though the flagellates transferred may linger for a week or more before 

 finally disappearing. Media which contain a comparatively large propor- 

 tion of human blood give better results than others, but the satisfactory 

 maintenance of T. gamhiense outside the body has not yet been accom- 

 plished. 



