86 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
recovered from an infection. And one guinea-pig (Experiment 2 1 6) which we infected with ' Gunjur ' 
strain was born from a guinea-pig infected at the time (also with ' Gunjur' strain). There is a certain 
amount of natural immunity or resistance to the human trypanosome to be met with in individual rats 
and other animals. Every now and then we have come across animals which have exhibited this feature. 
For example, of two rats A and B of the same size, inoculated at the same time with equal amounts of 
virulent blood from an infected animal, A will become infected while B remains uninfected or shows a 
prolonged incubation period. Again, A receives a larger dose than B ; it frequently happens that B will 
show the infection earlier than A. Guinea-pigs show considerable resistance to infection. As instances 
of this we would mention those inoculated from Rat 279A (see above). Baboons (Cynocephalus sphinx) 
have up to the present been absolutely refractory. 
Conclusions 
1. The trypanosomes found in (a) cerebro-spinal fluid of Uganda sleeping 
sickness cases, (F) cerebro-spinal fluid of Congo Free State sleeping sickness cases, (c) 
blood of Uganda trypanosome fever cases, and (d) blood of Congo Free State 
trypanosome fever cases, are all identical in animal reactions and morphology with 
Trypanosoma gambiense. The specific name gambiense (Button) must therefore for 
the future include the trypanosomes from the above-mentioned sources. 
2. There seems to be no acquired immunity against infection. 
3. There is no transmission of immunity to offspring. 
4. An animal which seems to have recovered may months later show parasites 
once more, apparently as the result of lowered vitality. 
