PLASMODIUM MALARIJE. 639 



veyed by means of the cattle tick from animal to animal. 

 The further the investigations have been pushed the 

 closer becomes the connection between mosquitoes and 

 malarial infection in man. So far as we know, a few 

 varieties of mosquitoes and man are the only places 

 where the malarial parasites develop, and Koch, fol- 

 lowing lines suggested by the work of others, has 

 now shown that the fresh cases of infection with 

 malaria occur only in warm weather when the parasites 

 can develop in the mosquitoes. Koch's idea is that 

 human beings having chronic malaria preserve in their 

 blood the malarial parasites during the cool months. 

 In the warm weather mosquitoes become infected, the 

 parasites develop in them and are present in their 

 poison sacs. These mosquitoes bite and infect fresh 

 human cases through subcutaneous inoculation. He 

 believes if we would treat all chronic malarial patients 

 with quinine so as to prevent the development of the 

 parasites and thus the infection of the new crop of 

 mosquitoes, we would prevent most, at least, of human 

 infection. 



Blood parasites are extremely common in cold- 

 blooded animals, fish, reptiles, and in birds. .Birds 

 appear to suffer from malarial infection similar to that 

 in man, and the parasites found in the blood-corpuscles 

 are closely allied to those of human malaria. But in 

 birds infection cannot be produced by subcutaneous or 

 intravenous inoculation with parasites from human 

 blood, nor can infection be transmitted from birds to 

 man. The blood parasites found in fish and reptiles, 

 though similar to, are not identical with, those found 

 in man, and they are not transmissible to man. This 

 source of infection may, therefore, be excluded. Ex- 



