142 TRYPANOSOMIASES OF RHODESIA. 



produce such profound pathological effects in the patient that the 

 remedy is almost as bad as the disease. 



Professor Ehrlich has recently entrusted me with the con- 

 duct of some experiments with a new trypanolytic, and I had 

 hoped to come here with a tale of another triumph to be added 

 to the list of successes of the eminent German scientist. The 

 experiments, I regret to say. are not yet completed. 



We have yet to seek an entirely satisfactory chemical remedy, 

 and I think it is to immuno-chemistry that we must tmrn, since 

 there are many indications that success will be met with in that 

 direction. Let us study these niiore closely. 



In the first place there is abundant evidence that there exists 

 naturally in the animal organism certain elements antagonistic to 

 trypanosomes. What these elements consist of is not known, 

 but they are found in the serum, and in certain organs such as 

 the spleen. 



For example, some species of animals offer great (resistance 

 to infection by certani species of trypanosomes — a feature of great 

 value in dift'erentiation. Man was held to be resistant to Trypano- 

 soma bnicci, and it was at one time thought that Tr. gamhicnsc 

 was non-pathogenic for the larger animals. Unfortunately, it 

 is now known that cattle and antelopes, in certain conditions, can 

 harbour this parasite. I have also shown that the so-called Tr. 

 rhodcsicv.se is more highly pathogenic for mules, sheep and small 

 laboratory animals than many of the animal trypanosomes. 



Theiler found that his Chai-Chai and Zululand trypanosome 



" proved not to be pathogenic for ever}- rabbit whicli was inoculated in 

 the first place and not at all for guinea pigs." 



I also found great difficulty in establishing a strain of the 

 trypanosome of Southern Rhodesia, my small laboratory animals 

 resisting inoculation with natural virus, but eventually becoming 

 infected after repeated inoculations or increasing doses, their re- 

 sistant elements probably becoming exhausted thereby. JNIoreover, 

 a strain once established appears to accommodate itself and be- 

 come subsequently infective with greater certainty, possibly be- 

 cause the trypanosome gains immunity against elements opposed 

 to it. 



Another Rhodesian trypanosome — namely Tr. 7'ivax — is only 

 pathogenic to equines and bovines ; laboratory animals have a 

 natural resistance to it. 



Laveran has recently stated that sheep readily become im- 

 mune or tolerant to trypanosomes, but sheep are for me the 

 most easily obtained and most suitable laboratory animals, and I 

 must admit I have never once found one of the fat-tail or half- 

 bred colonial variety resistant to or recover from airtificial in- 

 fection. Again, in chronic cases we find a balance established 

 between parasite and host. Game may harbour Tr. britcci and, 

 in some circumstances, Tr. (/ainbiciise unharmed ; their blood, 

 however, giving rise to a fatal infection when introduced into 

 a less resistant subject. "Fly-struck" cattle often acquire a 



