126 THE PHILOSOPHY 



they remain In a torpid ftate during the feverity of the feafon. For 

 protedtion and warmth, thefe animals, when they go into their win- 

 ter habitations, form, by means of a (lime or faliva that iflues from 

 every pore of their bodies, a membranous cover which ftops up the 

 mouths of their fhells. But this pellicle or cover, though apparent- 

 ly pretty hard and folid, is fo thin and porous as not entirely to ex- 

 clude the entrance of air, without which the principle of life could 

 not be continued. Accordingly, when, by accident, the pellicle is 

 made too thick, and prevents a communication with the external 

 air, the animal, to remedy the evil, makes a fmall aperture in its 

 cover. In this ftate fnails remain fix or feven months, without 

 food or motion, till the genial warmth of the fpring breaks their 

 flumber, and calls forth their adtive powers. Hence it fhould ap- 

 pear, that air is more neceflary to the prefervation of animal life 

 than food itfelf ; for, in numberlefs inftances, animals can live, not 

 for days or weeks, but for months, without fupplies of nourifhment. 

 None of them, however, are capable of exiftlng nearly fo long with- 

 out having fome communication with the air. 



With regard to fnails that live in frefh waters, or in the ocean, 

 the fpecies of which are numerous, their manner of refpiring is An- 

 gular. All of them have an aperture on the right fide of the neck. 

 This aperture ferves the complicated purpofes of difcharging the 

 faeces, of lodging the organs of generation, of afcending and de- 

 fcending in the water, and of refpiration. They are frequently ob- 

 ferved to ftraiten the orifice of this aperture, to ftretch it out in the 

 form of an oblong tube ; and, in this ftate, they rife to the furface, 

 in order to expel the former air, and take in a new fupply. 



But, though air feems to be an indifpenfible principle of animal 

 life, yrt many animals can live longer without the ufe of this ele- 

 ment, or at leaft with fmaller quantities of it, than others. Even 

 3 men, 



