white purulent discharge occurred from the eyes in both rabbits 
about the seventh day after inoculation. Simultaneously with this 
affection of the eyes the skin at the roots of the ears became 
encrusted with scabs. Both rabbits became drowsy early in the 
disease, and remained so until death. Although the incubation 
period in the case of rabbits was long (nine days), yet the animals 
early succumbed to the effects of the disease, in spite of the fact 
that the trypanosomes were never very numerous in the peripheral 
blood. 
Rats also showed drowsiness during the latter hall of the 
infection, while guinea-pigs continued to be lively and to take food 
well until a day or so before death, when in some cases drowsiness 
ensued. 
In our experiments we did not observe any marked relation 
between the colour of the animal inoculated and the duration of 
infection in that animal. (It is sometimes thought that white rats 
are less resistant than piebald.) 
In passing it may be noted, as has been done before, that the 
temperature of the host tended to rise with increase in the number 
of trypanosomes in the peripheral blood. 
EXPLANATION OF THE PERIODIC INCREASE AND DEC 
IN THE NUMBERS OF TRYPANOSOMES IN THE 
PERIPHERAL BLOOD OF THE HOST 
We believe that periodic increase and decrease of the num 
of trypanosomes in the peripheral blood of the host is a natui 
phenomenon, resulting from the reaction of the host and paiasite on 
each other. 
The parasites increase by longitudinal division until a max 
is reached when, unfavourable conditions arising, the formati 
rounded, latent, non-flagellate bodies occurs, especia y in 
internal organs of the host where they collect in the sp ee 
bone marrow during the period of decrease of flage ates 
peripheral blood. These rounded bodies, or at least some 
become flagellate trypanosomes when the parasites regm 
in numbers again (see Fantham (1911^ - _ 
tProc. Rov. Soc.. B, Vol. LX Will. pp. 21 2-227. and Ann. I r "P 
PP- 465-485. 
Med. and Parasitol., Vol. IV. 
