TRYPANOSOMES, TRYPANOSOMIASIS, AND SLEEPING SICKNESS 15 
Rats, mice, dogs, cats, guinea-pigs, and monkeys develop the disease in equally short 
incubation periods. Death occurs early: in the dog in nine days; cats, twenty days; 
rats, twelve to eighteen days ; mice, twelve to sixteen days ; monkeys, ten to twenty-four 
days. Guinea-pigs may die in twelve days to three weeks after the appearance of the 
parasites in the peripheral blood. The guinea-pig may resist, and after an incubation 
of three to five weeks acquire a more chronic form of the disease. 
Monkeys 
Various species have been used, Macacus rhesus, Cercopithecus callithricus y Cerco- 
pithecus ruber, Pithecia satanas (Jew and Sooty monkeys). All react to inoculation 
with almost the same sensitiveness. The Sooty appears to be somewhat less so, the 
parasites are rarely seen but autoagglutination of the corpuscles, anaemia, fever, and 
loss of weight occur as in the others. Monkeys, though reacting so well and the 
parasites often showing in large numbers, are, unfortunately, extremely liable to 
digestive disturbances, their vitality is not great and they quickly succumb to the 
complication. As they usually harbour large numbers of intestinal parasites the blood 
counts cannot be absolutely depended on. The monkeys infected with sleeping 
sickness strains have not shown any more symptoms of 'sleep' than others inoculated 
with 'Gunjur,' etc., strains. Monkeys infected with T. dimorphon and non-infected 
ones dying from dysentery, etc., have sometimes exhibited even more pronounced 
symptoms. 
It is of interest to record the progress of the disease in large animals infected 
for a long time. 
Horse VII 
Experiment No. 87. Inoculated by Button and Todd, February 14, 1903. 
Strain 'Mr. Q' (European, Senegambia). Parasites appeared March 16. Up to May, 
when it was sent to England, the organisms were fairly constant in the peripheral 
blood. From August 31, 1903, the blood was negative to microscopical examination, 
but still infective if inoculated in large amounts. On numerous occasions, the blood 
was centrifuged, but no parasites could be found. The blood when inoculated in 
amounts of 0*5 c.c. into rats and mice, formerly proved infective, such a quantity is 
at present of no use ; 2-5 to 3-0 c.c. or more is now needed to produce an infection. 
Moreover, it is necessary to use more than one animal, as the animal may only 
acquire a mild chronic infection with very few parasites to be seen in its blood. The 
horse, shortly after the infection, lost flesh but improved after arrival in England. It 
is now in excellent condition, weight, 510 pounds, no oedema. The blood count : 
reds, 5,600,000; whites, 17,600; haemoglobin, ninety per cent. Urine normal. 
The autoagglutination of the blood corpuscles is still present. Its temperature has 
been recorded for nearly the whole period (see chart) ; glandular enlargement has not 
been noticed since the animal arrived in England. 
