OF NATURAL HISTORY. 25 



ment of animals and vegetables are cfFeded. But I (hall confine 

 myfelf, at prefent, to fuch remarks as ar€ purely analogical, and 

 may be fully underflood without a minute knowledge of the diffe- 

 rent ways by which growth and nourifliment have been fiippofed 

 to be accompliflied. 



Animals, like vegetables, gradually expand from an embryo or 

 gelatinous ftate, and, according to their kinds, arrive fooner or later 

 at perfedion. This expanfion and augmentation of fubflance is the 

 idea conveyed by the word groivth. Without fome nutritious mat- 

 ter taken into the body, and affimllated, by the action of veffels, to 

 the fubftance of the being that receives it, growth cannot lake place. 

 Moifture is the chief food of plants. But the food of animals, in 

 general, varies with the fpecies. This faifl led fome philofo- 

 phers to conclude, that every plant extracted from the foil a food 

 peculiar to its own nature. It Vv^as, however, afterwards difco- 

 vered, by repeated experiments, that vegetables can grow, and 

 acquire a very confiderable degree of bulk and weight, without 

 exhaufting a perceptible quantity of the earth in which they are 

 planted. Thefe experiments are a fufficient proof, that molilure 

 conftitutes the chief nourilhment of plants. They likewife indi- 

 cate, that vegetables, however diverfified in their figure, denfity, and 

 fibrous arrangement, are more fimple in their texture than animals. 

 But, notwithftanding thefe feeming differences in the nourifliment 

 of plants and animals. Nature fails not to obferve the fune courfe 

 in both kingdoms. The food of the animal, before it is converted 

 into nourifliment, muft go through the intricate procefs of digeftion. 

 But, after the food has been converted into chyle, and the chyle into 

 blood, this blood becomes a common fluid, from which all nourifli- 

 ment and all animal fluids are derived. Here the analogy is appa- 

 rent. Moifture is to the plant precifely what blood is to the animal. 

 Each of them extrads its nourifliment from a common fluid j and) 

 t D in 



