Natural Infection, Pathogenesis. gQl 



somes may undergo sexual propagation in the insects as inter- 

 mediate hosts, as appears probable from recent investigations 

 (see p. 799), there would be a possibility that they may harbor 

 the parasites in their bodies for a longer time, and in the mean- 

 time transmit it to susceptible mammals. 



The infection results apparently only exceptionally through 

 fresh wounds in the skin and mucous membranes, whereas an 

 infection through the uninjured mucous membrane of the diges- 

 tive tract, as it was accomplished experimentally by Yakimoff 

 & Schiller, has not been observed. 



Pathogenesis. As trypanosomes are ahvays present in the 

 blood plasma and the tissue fluids, they apparently exert their 

 pathogenic action only indirectly by the production of toxic 

 products, which principally cause the destruction of the red 

 blood corpuscles, and thereby anemia. They probably influence 

 the metabolism of the host in other harmful ways. The fever, 

 the marked emaciation (with good appetite!), as well as the 

 affection of the nervous system (neuritis, later degeneration) 

 can be explained only by a toxic action, but it has so far not 

 l)een possible to demonstrate the supposed toxins of the 

 trypanosomes objectively (Laveran, Mesnil, Mayer and others). 

 The fact however that the parasites multiply outside of the 

 animal body only on media containing a great amount of hemo- 

 globin appears to indicate that they require hemoglobin, and 

 the destruction of the erythrocytes may be explained by the 

 fact that they abstract this substance from them. 



Following the infection a marked increase of trypanosomes 

 in the blood occurs periodically in the animals, and this is 

 usually accompanied by an elevation in temperature. Then 

 again they disappear rapidly, only to return again in great 

 numbers after a longer or shorter time, having proljably matured 

 meanwhile in certain organs (spleen, bone marrow?) from the 

 young forms. Their disappearance is according to the investi- 

 gations of Massaglia and Eodet & Vaillet, supposed to be due 

 to trypanolytic substances, which appear in the blood of in- 

 fected animals and the quantity of which increases until the 

 crisis. To what extent the leucocytes participate in this has 

 not yet been determined; as a matter of fact their number 

 greatly increases during the disease simultaneously with a 

 hyperplasia of the spleen, and a great number of leucocji;es 

 which contain in their bodies broken-down products of trypano- 

 somes are to be found in the spleen tissue, as well as in the 

 bone marrow. 



General Symptoms. They appear after a longer or shorter 

 incubation period, and excluding the acute and peracute cases, 

 which are manifested under severe febrile symptoms, consist 

 in general in intermittent or recurrent fever, transitory or 

 constant edema of the lower parts of the body, and progressive 



