EVOLUTION OF HEAT. 623 



656. We have seen that in Man, as in the lower animals, exercise has a con- 

 siderable though a more limited effect in producing an elevation of temperature; 

 and that this is not merely due to the acceleration of the circulation is shown 

 by the fact that the exercise of a particular muscle will cause an increase in 

 tfce heat liberated from it ( 330). * It may be stated as a general fact, that 

 every change in the condition of the organic components of the body, in which 

 their elements enter into new combinations with oxygen, must be a source of 

 the development of Heat. And as we have seen that a considerable part of 

 the carbonic acid and water which are exhaled in Respiration, is formed within 

 the body by the metamorphosis of its own tissues, and that this metamorphosis 

 is promoted by the active exercise of the nervo-muscular apparatus, it follows 

 that in animals whose habits of life are peculiarly active, whilst the temperature 

 of the surrounding medium is sufficiently high to prevent its exerting any con- 

 siderable cooling influence over them, the combustive process thus maintained 

 may be adequate for the maintenance of the temperature of the body at its nor- 

 mal standard. This seems to be the case with the great Carnivorous quad- 

 rupeds of warm climates, and with certain races of Men who lead a life of 

 incessant activity like theirs. But whenever the cooling influence of the 

 atmosphere is greater, or the retrograde metamorphosis of tissue takes place with 

 less activity, some further supply of heat-producing material is required ; and 

 this is derived either directly from the food, or from a store previously laid up 

 in the body. Although the albuminous and gelatinous components of the 

 food may be made, by decomposition within the body, to yield saccharine and 

 oleaginous compounds, which serve as an immediate pabulum to the combus- 

 tive process, yet this metamorphosis involves a great waste of valuable nutritive 

 material ; and the needed supply is much more advantageously derived at once 

 from those farinaceous or oleaginous substances which are furnished in abun- 

 dance by the Vegetable kingdom, the latter also by the Animal. No reasonable 

 doubt can any longer be entertained, that the production of Heat by the com- 

 bustive process is the purpose to which these substances are destined to be 

 subservient in the bodies of Herbivorous animals and of Man; and the results 

 of experience in regard to their relative heat-producing powers are in precise 

 accordance with the indications afforded by their chemical composition ( 401). 



657. Our knowledge of the dependence of all the vital processes in warm- 

 blooded animals upon the Heat of their bodies, and of the dependence of their 

 calorifying power upon the due supply of material for the combustive process, 

 has received some remarkable additions from the experiments of M. Chossat 

 upon Starvation. 3 He found that Birds, when totally deprived of food and drink, 

 suffered a progressive, though slight, daily diminution of temperature. This 

 diminution was not so much shown by a fall of their maximum heat, as by an 

 increase in the diurnal variation, which he ascertained to occur even in the nor- 

 mal state ( 651, 6). The average variation in the inanitiated state was about 

 6 (instead of 1J), gradually increasing as the animal became weaker; more- 

 over, the gradual rise of temperature, which should have taken place between 

 midnight and noon, was retarded; whilst the fall subsequently to noon com- 

 menced much earlier than in the healthy state; so that the average of the whole 

 day was lowered by about 4 2 between the first and the penultimate days of this 



1 It was affirmed by Dr. Granville ("Phil. Trans.," 1825) that the temperature of the 

 uterus during parturition sometimes rises as high as 120. In some observations made at 

 the Philadelphia Hospital, however, at the desire of Prof. Dunglison, the temperature of 

 the uterus was not found to be much above that of the vagina ; the former being, in three 

 cases, 100, 102, and 100, whilst the latter was 100, 100, and 105. (Prof. Dunglison's 

 "Human Physiology," 7th edit., vol. ii. p. 226.) 



2 "Recherches Experimentales sur 1'Inanition," Paris, 1843; an analysis of this work 

 will be found in the "Brit, and For. Med. Rev.," April, 1844. 



