REPORT OX AIOSOUITOES. 69 



they are injected, with the secretion, into the first person the 

 Anopheles bites, and after a short period of incubation that 

 individual comes down with malaria." 



When the sporozoits, or blasts, as they are also termed, are 

 introduced intO' the circulation, each enters a red blood corpuscle 

 and develops into a Plasmodium, exactly as if it had been one of 

 vegetative spores. The fact that there is an apparent period of 

 incubation is explainable by the small number of org"anisms 

 introduced which are not sufficient to produce a characteristic 

 "chill." 



How long the sporozoits retain their vitality within the mos- 

 quito is not known ; but there is no reason why the same mos- 

 quito should not infect several persons, since experiment has 

 proved that an individual will bite several times. Dr. Johnson 

 records a specimen in captivity which bit him four times at interr 

 vals of two or three days. A specimen of Anopheles disturbed 

 after biting and before feeding has already inoculated a victim 

 and has an appetite whetted for blood which she may satisfy 

 from another individual. 



As the Plasmodiiun requires for its development within the 

 mosquito body a period of from seven to ten days, the mosquito 

 to be able to transmit the disease must bite after the sporzoits 

 are developed. If it should bite even the day before and not 

 again afterward the disease would not be transmitted. Any 

 specimen that makes what would be normally its last meal on 

 malarial blood will fail as a carrier. 



Not all persons, though they may be suffering from genuine 

 malaria, are in a condition to infect mosquitoes. There must be 

 gametes in the blood in sufficient number to get into the peri- 

 pheral circulation, so that a biting mosquito may get some of 

 them. The malarial parasite lives through the winter in the 

 human blood; it can live no other way, because the hibernating 

 females do not feed before they go into winter quarters. That 

 point has been satisfactorily demonstrated by Dr. Johnson, and. 

 my own observations bear him out to the full. It is quite likely, 

 however, that individuals may bite during the winter in a warm 

 house, for they become active very readily under the influence of 

 even a moderate temperature. 



On the other hand, there is every reason to believe that the 

 organism may lie dormant in an individual for a considerable 

 period, becoming active again when the physical condition of 

 the host is favorable. Such individuals, too, may have the 

 gametes present in the blood, even though not actually sick, and 

 they may serve to start the disease in localities previously exempt. 

 Several instances of that kind have come to my notice, where 



