August 24, 1906.] 



SCIENCE. 



233 



Colonel David Bruce to do so by conveying 

 by its bite the Trypanosoma from wild big- 

 game animals, to the domesticated horses 

 and cattle of the colonists. The discovery 

 of the parasite and its relation to the fly 

 and the disease was as beautiful a piece of 

 scientific investigation as biologists have 

 ever seen. A curious and very important 

 fact was discovered by Bruce — namely, 

 that the native big game (zebras, antelopes, 

 and probably buffaloes), are tolerant of the 

 parasite. The Trypanosoma grows and 

 multiplies in their blood, but does not kill 

 them or even injure them. It is only the 

 unaccustomed introduced animals from 

 Europe which are poisoned by the chemical 

 excreta of the Trypanosomes and die in 

 consequence. Hence the wild creatures — 

 brought into a condition of tolerance by 

 natural selection and the dying out of those 

 susceptible to the poison — form a sort of 

 'reservoir' of deadly Trypanosomes for the 

 Tsetze flies to carry into the blood of new- 

 comers. The same phenomenon of 'reser- 

 voir-hosts' (as I have elsewhere called 

 them) has since been observed in the case 

 of malaria; the children of the native 

 blacks in Africa and in other malarious 

 regions are tolerant of the malarial para.- 

 site, as many as 80 per cent, of children 

 under ten being found to be infected, and 

 yet not suffering from the poison. This is 

 not the same thing as the immunity which 

 consists in repulsion or destruction of the 

 parasite. 



The Trypanosomes have acquired a ter- 

 rible notoriety within the last four years, 

 since another species, also carried by a 

 Tsetze fly of another species, has been dis- 

 covered by Castellani in cases of sleeping 

 sickness in Uganda, and demonstrated by 

 Colonel Bruce to be the cause of that awful 

 disease. More than 200,000 natives of 

 Uganda have died from it within the last 

 five years. It is incurable, and, sad to re- 

 late, not only a certain number of Euro- 



pean employees have succumbed to it in 

 tropical Africa, but a brave young officer 

 of the Army Medical Corps, Lieutenant 

 Tulloch, has died from the disease acquired 

 by him in the course of an investigation 

 of this disease and its possible cure, which 

 he was carrying out, in association with 

 other men of science, on the Victoria 

 Nyanza Lake in Central Africa. Lieuten- 

 ant Tulloch was sent out to this investiga- 

 tion by the Eoyal Society of London, and 

 I will venture to ask you to join that body 

 in sympathy for his friends, and admira- 

 tion for him and the other courageous men 

 who risk their lives in the endeavor to ar- 

 rest disease. 



Trypanosomes are now being recognized 

 in the most diverse regions of the world as 

 the cause of disease — new horse diseases in 

 South America, in North Africa, in the 

 Philippines and East India are all traced 

 to peculiar species of Trypanosome. Other 

 allied forms are responsible for Delhi-sore, 

 and certain peculiar Indian fevers of man. 

 A peculiar and ultra-minute parasite of the 

 blood cells causes Texas fever, and various 

 African fevers deadly to cattle. In all 

 these cases, as also in that of plague, the 

 knowledge of the carrier of the disease, 

 often a mite or acarus — in that of plague 

 the flea of the rat— is extremely important, 

 as well as the knowledge of reservoir-hosts 

 when such exist. 



The zoologist thus comes into closer touch 

 than ever with the profession of medicine, 

 and the time has arrived when the profes- 

 sional students of disease fully admit that 

 they must bring to their great and hopeful 

 task of abolishing the diseases of man the 

 fullest aid from every branch of biological 

 science. I need not say how great is the 

 contentment of those who have long worked 

 at apparently useless branches of science, 

 in the belief that all knowledge is good, to 

 find that the science they have cultivated 



