457 



on a healthy individual, or his food, water, milk, cooking utensils, 

 and so on. Some germs become detached from the insect's body, 

 and are thus conveyed from the sick to the healthy. In such 

 a manner are cholera, typhoid and other diseases due to patho- 

 genic bacilli spread by, for example, the common house-fly. This 

 being now proved beyond doubt, the only solution is prophylaxis 

 in the form of an organised wholesale destruction of this obnoxious 

 pest, both in its adult and larval forms. 



The third and most important group, that of insects which act 

 as intermediate hosts, was then dealt with. The lecturer said that, 

 while now the relationship between malaria and insects is looked 

 upon as almost axiomatic, the mere name of the disease alone 

 denotes that this was not always so. In 1894 Sir Patrick Manson 

 definitely formulated a hypothesis on the subject. In 1895 

 Major Sir Ronald Ross began his now classic investigations ; and 

 in some cases by direct evidence, in others by analogy, in the year 

 1900 the theory had passed from the region of conjecture to that 

 of fact. Ross in India, and others, including Grassi in Italy, 

 traced the development of the malaria parasite from man through 

 its various stages in the mosquito, back again to man ; so that 

 by the work of these and many other investigators the connec- 

 tion between mosquitoes and malaria was firmly established. An 

 enumeration of some other diseases similarly transmitted was 

 then given, and a list of the hosts responsible for their spread. 

 To mosquitoes are due : (a) Yellow fever, (b) elephantiasis, and 

 (c) dengue in' man, (d) horse -sickness in the Transvaal, and (e) 

 filariasis in man. The tsetse-fly is responsible for (a) sleeping sick- 

 ness in man and {b) nagana in horses and cattle. The Tabanidae 

 cause surra in cattle ; Stomoxys, mal de Caderas in horses ; 

 Hippobosca, galzieht in cattle ; fleas transmit plague ; sand-flies, 

 pappataci fever in man ; ticks, relapsing fever in man, and Texas, 

 Red water, Rhodesian, Heart water, biliary and other fevers in 

 cattle, horses and sheep ; spirochaetosis in fowls, and malignant 

 jaundice in dogs. And who can say how many more ? 



Some remarks were then made on elephantiasis, plague, yellow 

 fever, relapsing fever and sleeping sickness. In dealing with 

 yellow fever, it was stated that so far all attempts to discover the 

 actual parasite which causes this disease have proved futile ; but, 

 whatever may be the reason for this, it is practically admitted on 

 all sides that it is a micro-organism, most probably protozoal. It 



