XiV PRELIMINABY DISCOURSES. 



An Animal, endowed with sensibility and the power of motion, 

 can select the food necessary for his subsistence, and go in quest 

 of it, when he does not find it in his immediate vicinity; and can 

 seize it, in order to appropriate it to himself. He can, consequently, 

 nourish himself with various kinds of matter, even with kinds 

 which are but partially distributed in nature being such as are 

 already organized. 



A Plant, on the contrary, being unable to distinguish what is 

 proper for its sustenance, or to seize any kind of prey, must neces- 

 sarily nourish itself with matters which are so generally diffused 

 over the globe as to be found almost every where ; which are suf- 

 ficiently inert to oppose no resistance to the feeble means of absorp- 

 tion with which it is provided, and sufficiently soft and yielding 

 to require no mechanical division. Consequently, there are none 

 but inorganic substances such as water, air, and matters which 

 are soluble in those two vehicles adapted to that purpose ; and these 

 are, in fact, the substances which serve for the nutrition of plants. 



Animals, then, can select for their nourishment, a great variety 

 of matter, and consequently, the organs of their nutrition must 

 present a corresponding diversity : Vegetables, on the other hand, 

 are nearly all subsisted on the same materials, and therefore, 

 their organs of nutrition are very nearly similar. 



Animals, which select their food, often experience intervals in 

 which they are unable to procure such as is suitable for them ; and 

 when they do find it, they lay in a provision to last them for a 

 time. It is necessary, then, that they should be furnished with a 

 receptacle in which to deposit their store of nourishment: thia 

 receptacle is called the stomach. Plants, being constantly surrounded 

 by their appropriate aliment, and never changing their position, 

 have no necessity to lay in a stock of provisions, and accordingly 

 have no stomach in which to receive it. 



The nourishment of Animals being deposited in an internal cavity, 

 all the vessels of the animal are found converging toward that 

 centre : But in Plants, the absorbing vessels are directed toward 

 the surface. Animals, says BOERHAAVE, are nourished by internal 

 roots, and Plants by external roots : Consequently, the structure 

 of vegetables will be calculated to multiply surfaces, and will be 

 perfect in proportion as it is fitted to accomplish that object. The 

 organic structure of animals, having a central tendency, will be 

 perfect in proportion to the perfection of their internal organization. 



Inasmuch as the essential seat of nutrition, in Animals, is placed 

 in the interior and as the vessels are all directed toward and about 

 that centre, those vessels must continue to perform the same 



