OF WASHINGTON, VOLUME XV, 1913 111 



cies of Anopheles. I am, however, unwilling to believe that a species 

 of Anopheles which is peculiar to uninhabited forests and under nor- 

 mal conditions can not obtain human blood should forthwith be- 

 come the host of a blood-parasite of man. It is true that such a 

 case might occur and that we may have it before us in the one under 

 discussion, but in my opinion this would be so exceptional that it 

 would have to be very fully proven. 



There is every indication that the host-relation between the ma- 

 larial parasites and certain species of Anopheles is conditioned by 

 a very fine physiological adjustment. Thus it has been commonly 

 observed that of a number of species occurring in a given local- 

 ity and all obtaining their blood-meals from the same source, some 

 serve as efficient hosts for the parasites while other species simply 

 digest the parasites with the blood. Very often the commonest 

 Anopheles of a region will not be the one to serve as host. This 

 is the case, for example, with our Anopheles punctipennis, and 

 it is well established that A. rossi holds a similar relation in the 

 Orient. James and Liston may be quoted to good advantage in this 

 connection: 



We have already mentioned that some species of "anopheles" are better 

 malaria-carriers than others, and apart altogether from the fact that "ano- 

 pheles" may be abundant in a place without there being any malaria at all, 

 it often happens that the species which is present most abundantly is not the 

 one which is carrying malaria at the time. It is, however, a difficul t matter 

 to estimate the relative abundance of different species in any place, for some 

 are much more easily seen than others, and the habits which some species 

 have of secreting themselves among the straw of a thatched roof and of rest- 

 ing only upon objects which are as nearly as possible the same colour as they 

 are themselves, are very important. In order to exemplify this, it seems 

 worth while to recount an instance which happened in our experience. In 

 the malarious village of Ennur in the Madras Presidency, A . rossi was so 

 abundant that on almost every straw of the thatched roof of every house 

 three or four specimens of this species were resting. A careful search in the 

 ordinary way did not reveal the presence of any other species, and it is cer- 

 tain that, had there been no other object in the search than the mere deter- 

 mination of the species of "anopheles" present in the village, the observer 

 would have gone away quite satisfied that A. rossi was alone present. But 

 the village was an extremely malarious one, and knowing that A. rossi was 

 an inefficient carrier of malaria in nature, he was unwilling to believe that 

 no other species was present in the houses. Fixing his mind, therefore, upon 

 the thought that he was looking for A. culicifacies and not A. rossi, he again 

 commenced the search with great care, and was rewarded not only by det <<<- 

 ing the presence of A. culicifacies, but by catching a sufficient number of 

 this species during several days' work, to prove that it was the species respon- 



