

INFLUENCE OF HEAT ON ANIMALS. 81 



carbon and hydrogen, taken in as food, are made to unite with oxygen 

 derived from the atmosphere. It is dependent, therefore, as to its 

 amount, upon the due supply of the combustible material on the one 

 hand, and of atmospheric air on the other. If the former be not fur- 

 nished either by the food, or by the fatty matter of the body (which 

 acts as a kind of reserved store laid up against the time of need), the 

 heat cannot be maintained ; and it is in part for want of power to digest 

 and assimilate a sufficient amount of this kind of aliment, that animals 

 of warm climates cannot maintain their temperature in colder regions. 

 On the other hand, if the supply of oxygen be deficient, as it is when 

 the respiration is impeded by diseased conditions of various kinds, there 

 is a similar depression of temperature. 



116. Now if, from either of these causes, the temperature of the body 

 of a Bird or Mammal (except in the case of the Jiybernating species of 

 the latter, to be presently noticed) be lowered to about 30 below its 

 usual standard, not only is there a cessation of vital activity, but a total 

 loss of vital properties ; in other words, the death of the animal is a 

 necessary result. This occurrence is preceded by a gradually-increasing 

 torpidity ; which shows the depressing influence of the cooling process 

 upon the functions in general. The temperature of the superficial parts 

 of the body is, of course, first affected ; the circulation is at first retarded, 

 causing lividity of the skin ; but, as the temperature becomes lower, the 

 blood is almost entirely expelled from the surface by the contraction of 

 the vessels, and paleness succeeds. At the same time, there is a gradu- 

 ally-increasing torpor of the nervous and muscular systems, which first 

 manifests itself in an indisposition to exertion of any kind, and then in 

 an almost irresistible tendency to sleep. At the same time, the respi- 

 ratory movements become slower, from the want of the stimulus that 

 should be given by the warm current of blood to the Medulla Oblongata, 

 which is the centre of those movements ; and the loss of heat goes on, 

 therefore, with increased rapidity, until the temperature of the whole 

 body is so depressed, that its vitality is altogether destroyed. 



117. But when there is a deficiency of the proper animal heat, the 

 vital activity of the system may be maintained by caloric applied by 

 external sources. This fact is of high scientific value, as giving the most 

 complete demonstration of the immediate dependence of the vital func- 

 tions of warm-blooded animals upon a sustained temperature ; and its 

 practical importance can scarcely be overrated. It rests chiefly upon 

 the recent experiments of Chossat, who had in view to determine the 

 circumstances attending death by Inanition, or starvation. He found 

 that, when Pigeons were entirely deprived of food and water, their 

 average temperature underwent a tolerably regular diminution from day 

 to day ; so that, after several days (the exact number varying with their 

 previous condition), it was about 4J lower than at first. Up to this 

 time, it seems that the store of fat laid up in the body supplies the 

 requisite material for the combustive process ; so that no very injurious 

 depression of temperature occurs. But, as soon as this is exhausted, 

 the temperature falls rapidly, from hour to hour ; and as soon as the 

 total depression has reached 29J or 30, death supervenes. Yet it was 

 found by M. Chossat, that when animals thus reduced by starvation, 



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