154 GNATS OR MOSQUITOES — CHAPTER VIII 



objectors is, however, entirely cut away by the truly crucial 

 experiments conducted in the London School of Tropical 

 ^Medicine under the direction of Dr. Manson which conclu- 

 sively demonstrate that malaria can be transmitted to man 

 through the agency of Mosquitoes. A number of Anopheles 

 were allowed to bite a patient suffering from tertian ague 

 in Italy. They were then transported to England and 

 made to bite two healthy young English students. Both 

 these gentlemen developed tertian malarial fever, and the 

 characteristic parasites of the disease were found in their 

 blood. 



It is difticult to find in this experiment any possible 

 source of fallacy. It is absolutely conclusive of the fact 

 that this is at the very least one of the methods of the 

 transmission and propagation of the disease ; and a very 

 little consideration will show any one conversant with the 

 data of parasitism that it is also necessarily the only one, 

 saving only by the intravenous injection of the blood of a 

 patient suffering from malaria into the vessels of a healthy 

 subject ; a method hardly likely to occur in nature. 



The reason for our assurance of this is that the malaria} 

 parasite requires two successive hosts — a human being and 

 a Mosquito — to attain sexual maturity and propagation. 

 In the blood of the fever patient it multiplies non-sexually ; 

 in the tissues of the Mosquito it does so sexually. Now 

 there are a large number of parasites which have an 

 exactly parallel history, the most familiar being that of the 

 tape-worm, which lives and multiplies asexually in herhivora 

 and other eaten animals, and passes its sexually mature life 

 in the carnivora, and other animal- eating animals. Just as 

 it is possible to introduce asexually multiplying malarial 

 protozoa mechanically into the veins of a healthy man, so 

 would it, doubtless, be practicable, in these days of abdo- 

 minal surgery, to lay open the intestine and introduce into 

 it a living tape-worm, which would, doubtless, continue to 

 thrive in its new host. But in the ordinary plan of nature, 

 the eggs discharged from the bowel of the eating-Q,mn\^\ are 

 discharged in situations when they are likely to be swallowed 

 by the eaten animal, and in the latter produce the asexually 



