Insects and Human Health 531 



had to be proved that in no other way could the malarial germ 

 be transmitted. 



6. The next step after the practical test is the acceptance of 

 the theory, for it now stands uncontradicted by all known facts. 

 In the case of malaria this acceptance leads to control of the 

 disease and the agency of its transmission. 



259. Control of malaria. Knowledge of the cause of mala- 

 ria and the way of its transmission opened up another field 

 for scientific investigation. It became necessary, since the 

 Anopheles mosquito had been proven guilty, to learn its life 

 history and habits in order that effective measures might be 

 employed to exterminate it. It was necessary also to dis- 

 cover how the parasite in the human system may be con- 

 trolled or destroyed. A study of the mosquito is outlined 

 in the following section. We here consider briefly the con- 

 trol of the disease and the prevention of its spread by animal 

 agencies. 



The parasite in the human system is destroyed by quinine, 

 the only known specific for the disease ; but since quinine is 

 not equally safe for all persons, it should be taken only when 

 prescribed. The patient should be isolated so that no mos- 

 quitoes can feed upon the blood, and thus becoming infective 

 agents, spread the disease. This is the only way of preventing 

 its transmission to healthy individuals. 



260. Malaria, a typical disease caused by protozoa. 

 Malaria is typical of all diseases known to be caused by animal 

 parasites and transmitted by animal agencies. Its wide geo- 

 graphical distribution has made it of primary interest to those 

 who labor to conserve as well as to restore the health of man- 

 kind. Its successful mastery justifies at least the following 

 practical suggestions. 



First. There is sufficient reason to believe that the means 

 will be discovered of destroying all pathogenic protozoa and 

 bacteria or of neutralizing their poisonous products or toxins 

 in the human system. This is now done in several diseases. 



