308 Major Bonald Boss [March 2, 



single case in which I think I had overlooked the parasites on the 

 first occasion), although large numbers of healthy birds were kept in 

 this manner. The result in the case of the sparrows which were 

 subjected to the bites of the infected gnats was different indeed. Out 

 of 28 of these, dealt with from time to time, no less than 22, or 

 79 per cent., became infected in from five to eight days. And, as in 

 the first experiment, all the infected birds finally contained very 

 numerous parasites. 



It was most interesting to watch the gradual development of the 

 parasitic invasion in these birds ; and this development presented 

 such constant characters that, apart from other reasons, it was quite 

 impossible to doubt that the infection was really caused by the 

 mosquitoes. The course of events was always as follows : The blood 

 would remain entirely free from parasites for four, five, six or even 

 seven days. Next day one or perhaps two parasites would be found 

 in a whole specimen. The following day it was invariably observed 

 that the number of the organisms had largely increased ; and this 

 increase continued until in a few days immense numbers were present 

 — so that, finally, I often observed as many as seven distinct parasites 

 contained within a single corpuscle ! Later on, many of the birds 

 died ; and their organs were then found to be loaded with the 

 characteristic melanin of malarial fever. 



I also succeeded in infecting on a second trial one of the six 

 sparrows which had escaped the first experiment ; and also a crow 

 and four weaver-birds ; and lastly, gave a new and more copious 

 infection to four sparrows which had previously contained only a few 

 parasites. 



These experiments completed the original and fundamental 

 observations on the life-history of the HaBmarncebidae in mosquitoes. 

 The parasites had been carried from the vertebrate host into the 

 gnat ; had been followed in their development in the gnat ; and had 

 finally been carried back from the gnat to the vertebrate host. The 

 theories of King, Laveran, Koch and Bignami, and the great 

 induction of Manson, were justified by the event ; and I have given 

 a detailed historical and critical account of these theories, and of my 

 own difficulties and experiences, in the hope of bringing conviction 

 to those who might, perhaps, otherwise think the story to be too 

 wonderful for credence. 



But work of great importance remained to be done. I had 

 intended, immediately after making this study of one of the parasites 

 of birds, to extend the investigation more fully to those of man — a 

 work which now presented no difficulty, since both the kind of 

 mosquito hospitable to them (^Anopheles) and the form of the parasites 

 in the mosquito were well known to me. Unfortunately I was 

 obliged to attend to other and less important duties, which kept me 

 fully occupied for several months — an interruption which practically 

 put an end to my own study of the mosquito-theory at a very 

 interesting point. No time, however, was really lost. In December 



