VARIATIONS IN POWER OP ABSTINENCE. 149 



certain object, and then in their as rapidly dying off. In this re- 

 spect they resemble the Fungi among plants. (BOTANY, 789.) 



152. There are great variations in the degree of power 

 possessed by animals of different species to sustain abstinence 

 from food, which appear to be related to their respective 

 habits of life ; such as most easily obtain a constant supply 

 of food being immediately dependent upon it, and vice versd. 

 Thus, among the Iarva3 of Insects, those that feed upon vege- 

 tables or dead animal matter (in the neighbourhood of which 

 their eggs are usually deposited by the parent) speedily die if 

 placed out of reach of their aliment ; whilst those that lie in 

 wait for living prey, the supply of which is uncertain, are able 

 to endure a protracted abstinence, even to the extent of ten 

 weeks, without injury. Again, carnivorous Birds and Mam- 

 mals are generally able to exist for some time without food ; 

 their natural habits leading them to glut themselves upon the 

 carcase of the animal they have destroyed, in such a manner 

 as to prevent them from requiring any new supply for some 

 time : thus the wild cat has been kept twenty days without 

 food, the dog has lived for thirty-six days in the same circum- 

 stances, and the eagle for a similar period. But some herbi- 

 vorous animals, such as the camel and the antelope, whose 

 habits are such as to keep them out of the reach of food for 

 several days together, are able to endure a similar abstinence ; 

 whilst among the insectivorous Mammals, which naturally 

 take food often, and but little at a time, the power of absti- 

 nence is much less, the mole, for instance, perishing in 

 confinement, if not fed once a day, or even more frequently. 



153. We have next to consider the different substances 

 used as food, in regard to their chemical composition ; and to 

 inquire for what purposes in the nutrition of the body they are 

 respectively destined. The Vegetable tissues are chiefly made 

 up of the three components, oxygen, hydrogen, and carbon ; 

 the oxygen and hydrogen having the same proportions as in 

 water. Their composition being thus nearly the same as that 

 of starch, gum, and sugar (into which, indeed, they may for 

 the most part be converted by a simple chemical process), 

 alimentary substances of this kind form a natural group to 

 which we may give the name of Saccharine (sugary). But in 

 many vegetable substances used as food, there is a considerable 

 quantity of oily matter, stored up in cells ; and the same kind 



