The Behavior of Trypanosoma Lewisi During the Early Stage of the Incubation Period in the Rat

Abstract

In previous experiments it was shown that when trypanosomes are injected into the peritoneal cavity of a rat they are absorbed by the lymphatic system, pass readily and uninjured through lymph nodes and appear promptly in lymph from the thoracic duct.1 It was also discovered, from concurrent experiments not heretofore reported, that following the injection of large numbers of adult trypanosomes into the body cavity of a rat the parasites may be recovered almost immediately from the peripheral blood of the animal and that they then remain in the circulating blood throughout the natural course of the infection. These early observations were of particular interest since they ran contrary both to our expectation and also to the apparently widely accepted conception of the development of trypanosomes early in the incubation period; namely, that these parasites, following their transfer to a noninfected rat, undergo a rapid process of reproduction for from 3 to 7 days somewhere in the body before their appearance in the peripheral blood. Further experiments, reported here, give added proof that this view is untenable. As will be seen, Trypanosoma lewisi, throughout the incubation period of the infection, is a parasite of the circulating blood in which multiplication first commences.