92 EXTERNAL CONDITIONS OF VITAL ACTIVITY. 



poisoned by verdigris mixed with the refuse tallow from the engine, 

 were taken out by wheelbarrowfuls. It is not improbable that the 

 unusual supply of aliment, furnished by the refuse grease that floats 

 upon these ponds (which would impede the cooling of the water, if it 

 were not consumed by the Pish), contributed with the high temperature 

 to this unusual fecundity. 



136. Although a very low temperature is positively inconsistent with 

 the continuance of vital activity, in Animals as in Plants, yet we find 

 that even very severe cold is not necessarily destructive of the vital 

 properties of organized tissues ; so that, on a restoration of the proper 

 amount of heat, their functions may continue as before. Of this we 

 have already noticed an example, in the case of frost-bitten limbs ; but 

 the fact is much more remarkable, when considered in reference to the 

 whole body of an animal, and the complete suspension of all its func- 

 tions. Yet it is unquestionably true, not only of the lowest and sim- 

 plest members of the Animal kingdom, but also of Fishes and Reptiles. 

 In one of Captain Ross's Arctic Voyages, several Caterpillars of the 

 Laria Rossii having been exposed to a temperature of 40 below zero, 

 froze so completely, that, when thrown into a tumbler, they chinked 

 like lumps of ice. When thawed, they resumed their movements, took 

 food, and underwent their transformation into the Chrysalis state. One 

 of them, which had been frozen and thawed four times, subsequently 

 became a Moth. The eggs of the Slug have been exposed to a similar 

 degree of cold, without the loss of their fertility. It is not uncommon 

 to meet in the ice of rivers, lakes, and seas, with Fishes which have 

 been completely frozen, so as to become quite brittle ; and which yet 

 revive when thawed. The same thing has been observed in regard to 

 Frogs, Newts, &c. ; and the experiment of freezing and subsequently 

 thawing them, has been frequently put in practice. Spallanzani kept 

 Frogs and Snakes in an ice-house for three years ; at the end of which 

 period they revived on being subjected to warmth. 



137. It does not appear, however, that the same capability exists, in 

 the case of any warm-blooded animals ; since if a total suspension* of 

 vital activity take place in the body of a Bird or Mammal for any length 

 of time, in consequence of the prolonged application of severe cold, re- 

 covery is found to be impossible. The power which exists in these ani- 

 mals, however, of generating a large amount of heat within their bodies, 

 acts as a compensation for the want of the faculty possessed by the 

 cold-blooded tribes ; since they can resist, for a great length of time (if 

 in their healthy or normal condition), the depressing influence of a tem- 

 perature, sufficiently low to produce a complete suspension in the acti- 

 vity of the latter. 



138. It only remains to say a few words regarding the degree of heat 

 which certain Animals can sustain without prejudice, and which even 

 appears to be genial to them. Among the higher classes, this range 

 seems to be capable of great extension. Thus many instances are on 

 record, of a heat of from 250 to 280 being endured, in dry air, for a 

 considerable length of time, without much inconvenience ; and persons 



* In the case of hybernating Mammals, the suspension is not total ; and if it be ren- 

 dered such, the same result follows as in other instances. 



