Page:Tropical Diseases.djvu/195

X] experiments the healthy rat contracted the infection; but if the transference was delayed, for an hour even, the experiment failed. As similar experiments with other blood-sucking flies (Stomoxys, for example) which, apparently, have no biological connection with T. brucei, succeeded to some extent, and as such a method of feeding can only occur exceptionally in nature, it is reasonable to infer that the closely allied T. gambiense is not usually

Fig. 46.—Trypanosoma gambiense: various forms from blood and cerebro-spinal fluid.

communicated in this purely mechanical way. We know that the malaria parasite can be communicated by the direct inoculation of malarial blood, but it is universally admitted that direct inoculation is not the natural method of transmission. The idea that the glossina inoculated trypanosomes in this direct way originated, undoubtedly, with the interpretation that has been placed on Bruce's experiments with nagana, an interpretation which may be incorrect. It is true that both Bruce and Minchin communicated trypanosoma infection