428 FUNCTIONS OF THE NERVES. [ch. iti. 



rating for the formation of the vital principle in man and many 

 animals, the vis nervosa seems to claim an important position, 

 since in many operations ascribed to the vital principle, the 

 function of the nerves is predominant. The nerves appear 

 also necessary to the application of nutrient material, and the 

 reproduction of cut off parts, because if the nerves of a part be 

 injured, its nutrition is impaired, and because the animals 

 which are tenacious of life and of irritability, also possess a 

 remarkable property of reproducing separated parts. 



Since vegetjibles and some animals generate, are nourished, 

 and reproduce cut-off parts, and, consequently, possess a vital 

 principle, although they appear to be destitute of a nervous 

 system, it follows that the vital principle may exist independently 

 of the vis nervosa in plants and certain animals not endowed with 

 nerves ; but it does not hence follow, that the vital principle can 

 exist without the vis nervosa in man and animals endowed with 

 a nervous system. For nature seems to have bound all parts 

 of our body together by such an agreement and combination, 

 that one part assists another, and one cannot easily exist without 

 another ; and especially the vis nervosa seems to be necessary 

 to the constituting of the vital principle in our own body and 

 in the bodies of animals endowed with a nervous system, 

 although it appears that the principle may exist without the 

 vis nervosa in plants and animals that have no nervous system. 

 There are certain animals and vegetables which reproduce their 

 kind without distinction of sex, but is the congress of both 

 sexes, therefore, not necessary to generation in man and other 

 animals and vegetables? 



