164 THE STORY OF GERM LIFE. 



ficial method yet devised. Its whole history is 

 therefore not known. It doubtless has some 

 home outside the blood of animals, arid very 

 likely it may pass through other stages of a meta- 

 morphosis in the bodies of other animals. Most 

 parasitic animals have two or more hosts upon 

 which they live, alternating from one to the other, 

 and that such is the case with the malarial para- 

 site is at least probable. But as yet bacteriolo- 

 gists have been unable to discover anything very 

 definite in regard to the matter. Until we can 

 learn something in regard to its life outside the 

 blood of man we can do little in the way of devis- 

 ing methods to avoid it. 



Malaria differs from most germ diseases in the 

 fact that the organisms which produce it are not 

 eliminated from the body in any way. In most 

 germ diseases the germs are discharged from the 

 patient by secretions or excretions of some kind, 

 and from these excretions may readily find their 

 way into other individuals. The malarial organ- 

 ism is not discharged from the body in any way, 

 and hence is not contagious. If the parasite does 

 pass part of its history in some other animal 

 than man, there must be some means by which it 

 passes from man to its other host. It has been 

 suggested that some of the insects which feed 

 upon human blood may serve as the second host 

 and become inoculated when feeding upon such 

 blood. This has been demonstrated with start- 

 ling success in regard to the mosquito (Anopheles], 

 some investigators going so far as to say that this 

 is the only way in which the disease can be com- 

 municated. 



Several other microscopic animals occur as 

 parasites upon man, and some of them are so 

 definitely associated with certain diseases as to 



