TRYPANOSOMIASES OF RHODESIA. I43 



tolerance to the organism, but in practice we frequently find 

 such a balance broken down under conditions unfavourable to the 

 animal — hard work, exposure to rains, starvation. Conversely, 

 when treating such animals, the most effective trypanolytic agents 

 will probably fail unless associated with favourable hvgieniic 

 conditions. 



These instances point to a very valuable " first line of de- 

 fence " in dealing with trypanosomes. and our modern knowledge 

 of vaccine-therapy suggests a method whereby this may be rein- 

 forced. It may be that the favourable results of drug treatment 

 have depended upon such principles rather than upon the steri- 

 lising effect of the agent. 



This paper is assuming such alarming proportions that I 

 will not go deeply into the subject of the symptoms of these 

 diseases. A few points, however, may be of interest. 



As I have said before, the animal trypanosomiasis of 

 Southern Rhodesia is, in the majority of cases, of a mild type, 

 a few animals only succumbing to the acute form and dying in 

 the early febrile stages. There seems to be some evidence that 

 the severity of the disease bears a relation to the extent to 

 which the animal has been submitted to infection — that is, as 

 far as we know, to the bite of the " tsetse fiy." 



One may divide the outbreaks into three categories : — 



1. In whiich the cattle have died rapidly and of the acute 

 form of the disease, generally those animals which have lived 

 in a " fly " area and have ibeen constantly submitted to infection. 



2. In which the cattle have died of the sub-acute or chronic 

 form of the disease, generally those animals wdiich have passed 

 occasionally through a " belt." 



3. A mixture of i and 2. generally in herds which have 

 lived on the edge of a " fly zone." Laboratory experiments seem 

 to support such an explanation. 



In this country, where African Coast Fever is always to be 

 feared, deaths of the first type are liable to cause alarm, as the 

 animal may die fat and without the usual symptoms of ansemia 

 and cachexia, commonly regarded as charaicteristic of " fly 

 disease." 



With iregard to the humaji trypanosomiasis of Rhodesia, 

 there is one feature which appears to support the opinion of 

 Stephens and Fanthan that it is a distinct entity, namely, the 

 quite extraordinary oedema of the face produced in infected sheep 

 and rabbits. 



In my sub-inoculations made with the W.A. strain this 

 symptom was most marked, and distinguislied sheep inoculated 

 with the human parasite from those inoculated with the animal 

 strains on Broken Hill or Southern Rhodesia. 



Recently I have, through the kind assistance of Doctors 

 MacKnight and Ellaconiib, been able to establish a strain of 

 human trypanosomiasis obtained from a patient infected on or 

 near the Luapula in the Congo. Up to the present neither sheep 



