ANIMAL PARASITES AND 

 HUMAN DISEASE 



CHAPTER I 

 INTRODUCTION 



ONE of the most appalling realizations with which every student 

 of nature is brought face to face is the universal and unceasing 

 struggle for existence which goes on during the life of every 

 living organism, from the time of its conception until death. 

 We like to think of nature's beauties; to admire her outward 

 appearance of peacefulness; to set her up as an example for 

 human emulation. Yet under her seeming calm there is going 

 on everywhere in every pool, in every meadow, in every 

 forest murder, pillage, starvation and suffering. 



Man often considers himself exempt from this interminable 

 struggle for existence. His superior intelligence has given him 

 an insuperable advantage over the wild beasts which might 

 otherwise prey upon him; his inventive genius defies the attacks 

 of climate and the elements; his altruism, which is perhaps his 

 greatest attribute, protects, to a great extent, the weak and 

 poorly endowed individuals from the quick elimination which is 

 the inevitable lot of the unfit in every other species of animal on 

 the earth. Exempt as we are, to a certain extent, from these 

 phases of the struggle for existence, we have not yet freed our- 

 selves from two other phases of it, war and disease. We have 

 some reason for hoping that after the present world-wide con- 

 flagration of war has burned itself out and its ashes, the flesh and 

 bones of its countless victims, have disintegrated and disappeared 

 from view, we may be able to free ourselves from the probability 

 of ever again taking part in or witnessing such a spectacle. 

 That the helpless bondage in which we were once held by disease 

 will never again be our lot, we can say with more assurance. 



1 



