35 



support the due arterialization of the blood -, and hence animals con- 

 fined in such air are in a state peculiarly liable to be affected by any 

 great or unusual depression of temperature. It is probably on ac- 

 count of their breathing air much contaminated by carbonic acid gas 

 that persons sleeping near limekilns are so frequently frost-bitten. 

 In repositories for animals which are much frequented the air is vi- 

 tiated by the respiration of the visitors also, who, moreover, impart a 

 heat to the rooms which is indicated by the thermometer, but is not 

 beneficial but noxious to the animals. The air should be continually 

 renewed, and when its temperature is to be raised it should be heated, 

 where practicable, by a furnace placed in a lower apartment previously 

 to being admitted into the repository, from which ample exit should 

 be allowed at the top : in this manner an effective ventilation on just 

 and scientific principles would be established. 



Exhaustion from fatigue is one of the causes which render persons 

 ascending heights more susceptible to the impression of cold : ex- 

 haustion from hunger produces the same effect : Mr. Hunter has 

 shown that an animal which had fasted for some time was more 

 affected by cold than one that was well fed, the reduction of tempe- 

 rature in the latter being 16° and 18°, in the former 18° and 21°. 

 The means of counteracting these effects in menageries are obvious ; 

 but it is particularly necessary to attend to them in the importation of 

 tropical animals, so many of which perish in beating up Channel, the 

 effect of the low temperature being increased by the exhaustion from 

 the fatigue of the voyage. Hence in the Channel not only should 

 cold be particularly guarded against, but additional food should be 

 supplied. 



Young animals are generally very susceptible of the effects of cold, 

 as has been shown by the experiments of M. Edwards. Thus, young 

 birds removed from the nest become quickly of the same temperature 

 as the surrounding atmosphere. The young of those Mammalia which 

 are born blind are equally obnoxious to cold, their blood being im- 

 perfectly arterialized, owing to the foramen ovale remaining open for 

 some time ; the young of the other Mammalia retain the temperature 

 of the adult animal. This makes it very important that if any of the 

 feline or similar races of animals breed in European menageries, their 

 dens should be peculiarly warm : the probability of preserving them 

 will also of course be considerably increased if the young are produced 

 in summer, or even in spring. 



Season, as has been shown by the experiments of M.Edwards, ex- 

 ercises a considerable influence on the susceptibility of animals for cold; 

 a much greater degree being borne with impunity in winter than in 

 summer. This is apparently analogous to what occurs in the vegetable 

 kingdom : a tree which will bear in winter a temperature of — 20° with- 

 out injury will be scathed as if by lightning, and perhaps die, if in sum- 

 mer it be exposed to 32° or 30°. Many animals, in captivity especially 

 (the Sylviadce as a familiar instance,) are as susceptible of cold as these 

 trees ; a draft of cold air or a frosty night will frequently produce on 

 them effects from which they never recover. As this susceptibility is 

 so considerably increased during summer, especial care should be 



