INTRODUCTION. XXiii 



the lowest degree in which, animal life does exist, or 

 possibly can exist, without a new order of things. 

 These qualities, sensation and motion, are of necessity 

 combined always; they constitute the first ingredients 

 in the composition of life, both in vegetables and ani- 

 mals, and by being modified in various ways by their 

 application to different organs, may be traced up to the 

 perfect animal, man. 



Nutrition is the first want of every being, and is one 

 of the modes of sensation; therefore, before any other ap- 

 paratus is provided for animal life, means are resorted to 

 to carry it on. Vegetables are fixed to the soil, and are 

 furnished with great numbers of porous roots, which by 

 spreading in different directions, come in contact with 

 the moisture of the ground and by simple absorption 

 conduct it as the aliment of the plant. There are many 

 animals which have a vegetative life almost as simple 

 as this, are fixed permanently to the spot where they 

 came into existence; others are permitted to change 

 their places of abode, and a provision for nourishment 

 by roots would not answer; hence comes the necessity 

 of a stomach, or reservoir in the interior of the body, 

 into which aliment may be introduced, and transported 

 along with the animal. In many instances this stomach 

 seems to constitute the whole animal, as in a hydatid : 

 it receives such simple fluids as compose the medium in 

 which it resides, and carries on its digestion, with so 

 little change of the alimentary matter, that there seems 

 to be nothing of an excrernentitious kind, as commonly 

 understood, thrown off. These animals are found abun- 

 dantly in the waters of tropical regions, exist sometimes 

 in the brain of man, and of sheep, in the uterus, and in 

 almost every part of the body. But, again, there are 

 stomachs of a more complex kind, which have opening 

 into them a great number of absorbing orifices, called, 

 in the striking language of Boerhaave, " genuine inter- 



