on Mosquito Extermination. 37 



germs outside the human system. His pupil, Dr. Ronald Ross, 

 at that time an English military surgeon, studying in London, 

 went to India in 1896 with the determination to discover the 

 insect concerned. After nearly two years of laborious experi- 

 ment, during which Ross reports that he must have dissected 

 "nearly a tliousand mosquitoes," he actually found a mosquito 

 of peculiar structure and external markings (Anopheles), in 

 whose stomach wall pigmented bodies appeared after such an 

 insect had bitten a malarial patient. The subsequent discov- 

 eries, in brief, are that the mosquito in question is born in- 

 nocuous and never shows such malarial bodies unless it has 

 itself first received them from a human being. If it has once 

 bitten an infected human being, the parasites from the patient's 

 blood may be found within 30 hours after to have settled upon 

 the insect's stomach wall ; they may be observed by dissection 

 of successive mosquitoes to grow day by day until on the 6th 

 or 8th day in favorable conditions of food and temperature 

 the parasites are visible under a low-power microscope, and 

 are seen to possess a thin transparent capsule, inside of which 

 immense numbers of minute sickle-shaped rods are gathered. 

 This capsule finally bursts, the rods are scattered in the general 

 body cavity of the host, and carried in great numbers to the 

 poison gland, from which they are injected, when the mosquito 

 next bites, into the blood of a new victim. The person bitten 

 sickens in about 14 days after the bite. This process, also, 

 though its observation involves many technical difficulties in 

 the laboratory, has been successfully worked out in various 

 parts of India, in South Africa, West Africa, Holland, Italy, 

 and the United States. A precisely similar process has also 

 been observed with another malarial parasite (Proteosoma) 

 peculiar to sparrows, canaries and certain other birds ; the 

 avian parasite is conveyed not by Anopheles but by certain 

 species of the Genus Culex. 



Experimental malaria has been voluntarily produced (Lon- 

 don, Italy, India) in persons not otherwise exposed to any 

 known cause of the disease, by the bite of infected insects. 

 The subject bitten had his first chill 14-17 days after the 

 bite. 



Negative evidence is that persons have experimentally lived 

 for several months (sleeping in wire gauze cottages) in the 

 most highly insalubrious sections of the Roman Campagna 



