REPORT OF THE SOCIETY ^ 99 



ANIMAL PARASITES AND RURAL S.\NITATION 



Dr. Wm. A. Riley, Cornell University 



When your worthy secretary asked me to speak before you this evening 

 it seemed, at first, that the subject of animal parasitism and its relation to 

 sanitation hardly had a place on the program of a society devoted to "the 

 protection of plants from insects and fungous diseases." On second 

 thought, I justify the invitation and my acceptance on the grounds that the 

 development of rural sanitation is one of the most important factors in the 

 safeguarding of the man and his family who must be directly responsible for 

 the protection of our agricultural products. I hope to show that in the 

 development of a rational sanitation the study of the life histories and the 

 biology of animal parasites is of prime importance. 



In taking up our subject it is necessary to define what we mean by the 

 term "parasite." This is not so easy as might, at first thought, appear. 

 It is often said that "a parasite is an organism which lives at the expense of 

 another." A little consideration will show that this definition is equally 

 applicable to a predatory species or, in its broadest sense, to all organisms. 



For the purpose of our discussion we may say with Braun, that; 



"A parasite is an organism which, during the whole or a part of its 

 life, lives on or in the body of another organism, from which it obtains its 

 sustenance." 



The infested organism is known as the host. In the case of many 

 parasites, a sexual stage is developed in one species of animal, and an 

 asexual stage is developed in an entirely different host-species. In such 

 instances we refer to the animal in which the parasite appears in its sexual 

 form as the primary host. The one in which the asexual stage of the parasite 

 occurs is the intermediate host. 



Of the many parasites which infest man and animals we shall consider 

 only those belonging to the animal kingdom and we shall still further limit 

 ourselves to a discussion of a few of those commonly referred to as "worms." 



The terms "parasites" and "parasitic worms" awake in the popular 

 mind only feelings of disgust and loathing. To the zoologist it is quite 

 different, for he soon loses all other feeling in one of amazement and appre- 

 ciation of the wonderful life histories of these animal forms, the amazing 

 ways in which they adapt themselves to their environment, and the devices 

 by which they are enabled to hold their own in the struggle for existence. 



