98 RESPIRATION. 



necessary to the preservation of animal life than food itself, 

 for, in numberless instances, animals can live, not for days or 

 weeks, but for months, without supplies of nourishment. 

 None of them, however, are capable of existing nearly so 

 long without having some communication with the air. 



With regard to the snails that live in fresh waters, or in 

 the ocean, the species of which are numerous, their manner 

 of respiring is singular. All of them have an aperture on the 

 right side of the neck, through which they respire. They 

 are frequently observed to straiten the orifice of this aperture 

 to stretch it out in the form of an oblong tube, and, in this 

 state, they rise to the surface, in order to expel the former 

 air, and take in a new supply. 



But, though air seems to be an indispensable principle of 

 animal life, yet many animals can live longer without the use 

 of this element, or at least with smaller quantities of it, than 

 others. Those animals which lie torpid during the winter, 

 as the hedge-hog, the dormouse, the marmot, &c., though per- 

 haps not .entirely deprived of all communication with the air, 

 exist, with only an occasional and interrupted respiration, till 

 the heat of the spring restores their wonted powers of life, 

 when a full respiration becomes again equally necessary as 

 before their torpor commenced. The toad, like all the frog 

 kind, is torpid in winter. At the approach of winter, it re- 

 tires to the hollow root of a tree, to the cleft of a rock, and 

 sometimes to the bottom of a ditch or pond, where it remains 

 for months in a state of seeming insensibility. In this last 

 situation it can have very little communication with the air. 

 But still the principle of life is continued, and the animal re- 

 vives in the spring. What is more wonderful, toads have 

 been found, in a hundred places on the globe, inclosed in the 

 heart of solid rocks, and in the bodies of trees, where they 

 must probably have existed for centuries, without any appa- 

 rent access either to nourishment or air ; and yet they were 

 alive and vigorous. 



These facts are supported by authorities so numerous and 

 so respectable, that it is unnecessary to quote them. Many 

 abortive attempts have been made to account for an animal's 

 growing and living very lonsj in the situations above de- 

 scribed, without the possibility of receiving nourishment or air ; 

 especially as, like all other animals, when put into an exhausted 

 receiver, it is soon destroyed. No satisfactory explanation, 

 however, has ever been offered ; and solitary exceptions like 

 these do not invalidate the general principle, that the respi- 



