18 ZOOLOGY. 



ing ; and finally, caeteris paribus, absorption will be less rapid 

 as the liquids to be absorbed are less liquid and less fitted to 

 moisten the tissues. 



OF DIGESTION. 



38. One of the principal means by which the absorp- 

 tion of the matters necessary for the nutrition of animals 

 is effected, is a cavity communicating with the exterior, and 

 into which the food is introduced. 



39. Aliments. We restrict the meaning of this term, 

 for the sake of clearness, to those substances which, being 

 introduced into the stomach, are absorbed only after being 

 digested. It is needless to remark that food and air are 

 essential to the support of Ijfe. 



The want of food is indicated by the painful sensation we 

 call hunger : its seat is in the stomach. This want and its 

 sensation may be diminished and kept off by rest, sleep, and 

 by whatever retards the vital movements. On the contrary, 

 it is increased by activity, fresh air, and by the use of bitters. 

 Hybernating animals, which sleep during winter, eat not, so 

 long as the lethargy continues ; and cold-blooded animals, 

 as fishes and frogs, can live in despite of a long- continued 

 abstinence. But man and other hot-blooded animals and 

 more especially, for an obvious reason, the young perish 

 speedily when food is withheld, even for a comparatively 

 short time. In Dante's celebrated episode of the destruction 

 of the Ugolini family by starvation, the youngest perished 

 first. 



All alimentary substances are furnished by the organic 

 kingdoms animal and vegetable ; whatever be their origin, 

 they may be divided into azotized elements, amylaceous or 

 sweet, and fatty bodies. These substances differ in their 

 nutrient qualities ; and it is a fact, prfrved by many curious 

 experiments, that a certain number of different substances is 

 essential for the support of life. 



Thus, rabbits fed upon only one article of food, as hay, 

 wheat, cabbage, carrots, &c., die in about fifteen days ; whilst 

 fed on these articles combined or given in succession, they 

 live and thrive. 



A hygienic law, then, is, the diversity and variety in 

 respect of food ; and experience and experiment agree as to 

 this. 



