ANIMAL AND VEGETABLE PARASITES. 539 



on killing the dogs, at various periods after the meal, from three 

 hours to eight weeks, he found the cysticerci in various stages of 

 development in the intestine, and finally converted into the full 

 grown Taenia, with complete articulations and mature eggs. 



Dr. Kuchenraeister 1 has also performed the same experiment, with 

 success, on the human subject. A number of cysticerci were ad- 

 ministered to a criminal, at different periods before his execution, 

 varying from 12 to 72 hours ; and upon post-mortem examination 

 of the body, no less than ten young ta3nia3 were found in the 

 intestine, four of which could be distinctly recognized as specimens 

 of Taenia solium. 



Finally, both Leuckart and Kuchenmeister* have shown, on the 

 other hand, that the eggs of Ta3nia solium, introduced into the body 

 of the pig, will give rise to the development of Cysticercus cellulose ; 

 thus demonstrating that the two kinds of parasites are identical in 

 their nature, and differ only in the manner and degree of their 

 development. 



There remains, accordingly, no good reason for believing that 

 even the encysted parasites are produced by spontaneous genera- 

 tion. Whatever obscurity may hang round the origin or reproduc- 

 tion of any class or species of animals, the direct investigations of 

 the physiologist always tend to show that they do not, in reality, 

 form any exception to the general law in this respect ; and the only 

 opinion which is admissible, from the facts at present within our 

 knowledge, is that organizedleings, animal and vegetable, wherever they 

 may be found, are always the progeny of previously existing parents. 



1 On Animal ard Vegetable Parasites, Svdeiih.aiu transition : L^rdon, 1857, 

 p. 115. 



2 Up. cit., p. 120. 



