334 PARASITIC DISEASES. 



A reaction occurred amongst pathologists, and as many pro- 

 ducts supposed to be parasitic proved to be nothing of the 

 sort, it was supposed that entozoa existed in the bodies 

 of men and animals for some wise purpose, and excited the 

 secretions, favoured digestion, &c. Amongst veterinarians 

 Bracy Clark advocated such views early in the present 

 century, and went so far as to recommend horsemen to 

 give their horses some of the germs of oestrus equi, that 

 their stomachs might not be deprived of the healthy stimulus 

 which they enjoy in a state of nature from the usual system 

 of propagation of these parasites. Bracy Clark thus advo- 

 cated doctrines which had been defended by no less eminent 

 naturalists before, such as Gotze and Abildgaard. 



It was supposed by others that parasites developed in ani- 

 mals previously diseased, and that a predisposition had to be 

 acquired by a certain state of ill health for the production of 

 any parasitic malady. 



We now know that parasites are not generated in certain 

 morbid conditions, and do not exist in animals to excite the 

 normal functions of their organs. They are offensive pro- 

 ducts foreign to the bodies of the men and animals they 

 afflict, and dependent entirely for their development on the 

 introduction of germs into bodies suited to their growth, pro- 

 tection, and reproduction. 



A few parasites exist in or on all human beings and ani- 

 mals, but certain parasitic animals and vegetables induce 

 actual disease, and often diseases of a very fatal nature. 



The manner in which entozoa injure and destroy is not 

 always the same. Some induce disease and irreparable struc- 

 tural changes in important organs, from their mere growth 

 and multiplication in those organs. Thus the brain of the 

 ox or sheep is destroyed by coenuri and echinococchi. The 

 latter parasites and flukes lead to destruction of the livers 



