PLASMODIUM MALARIL. 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- 
