ANIMAL HEAT. 



683 



simple conditions. These conditions them- 

 selves are, in the first place, assumed from 

 comparisons of the organization of the two 

 grand groups or series into which the animal 

 kingdom is divided with reference to heat 

 the cold-blooded animals, and the warm- 

 blooded animals. In this review we have 

 avoided all hypothesis, confining ourselves to 

 the severe method of deduction, always starting 

 from well-authenticated facts, and even con- 

 firming each step in advance by new data 

 equally indisputable. The hurmony which 

 reigns in this comprehensive whole", which 

 embraces the different classes of animals and 

 man, not only in the various modifications of 

 health, but even of disease, in their relation 

 to external agents, and the therapeutic pro- 

 cesses of nature and of art, afford the surest 

 confirmation of the reality of these relations. 

 As the phenomena of animal heat are re- 

 ferable to two general conditions of the eco- 

 nomy, the state of the blood and that of 

 the nervous system ; and as we have only in 

 the first instance deduced these from the com- 

 parison of natural facts, although we have 

 confirmed them by new observations and par- 

 ticular experiments, one may be desirous of 

 seeing them confirmed by experiments of a 

 more general bearing. To the reasonableness 

 of this wish we yield assent the more willingly, 

 as the results we have to quote are deductions 

 from some of the most admirable researches 

 that have been instituted by physiologists; 

 I allude to the enquiries of Legallois, Sir 

 Benjamin Brodie, and Dr. Chossat. 



The first of these experimenters, by the em- 

 ployment of various means for impeding re- 

 spiration, or limiting the consumption of air, 

 found that the refrigeration of animals is in 

 the compound ratio of the difficulty experienced 

 in breathing and of the quantity of oxygen con- 

 sumed ; so that when, in two experiments, the 

 d(fficulti/ of breathing is the same, the greatest 

 extent of cooling occurs in that in which the 

 smallest quantity of oxygen is vitiated, and the 

 contrary. Now, the end of the process of 

 respiration being to change the venous into 

 arterial blood, this conclusion of Legallois con- 

 firms directly the one of the two principal 

 conditions THE STATE OF THE BLOOD, which we 

 have laid down as influencing the production 

 of heat among animals, and to the knowledge 

 of which we had attained by induction. 



The results of the direct experiments which 

 we have still to quote also come powerfully 

 in aid of our inferences concerning the other 

 principal condition, which we have assumed 

 from induction, influencing the production of 

 animal heat: this is THE STATE OR ACTION OF 



THE NERVOUS SYSTEM. 



Sir B. Brodie demonstrated by a series of 

 the most ingeniously conceived and happily 

 executed experiments, that when animals were 

 decapitated and respiration was kept up by 

 artificial means, so that the blood circulated 

 as usual, and the process of change from the 

 venous to the arterial state went on uninter- 

 ruptedly, the ordinary quantity of carbonic 

 acid being eliminated, all the while, that, ne- 



vertheless, the temperature fell rapidly, even 

 more rapidly than when no artificial respiration 

 was maintained. 



Dr. Chossat completed these researches upon 

 the nervous system in its relations with the 

 production of heat, by demonstrating in a 

 series of experiments the following very im- 

 portant fact, viz. that the depression of animal 

 heat is constantly in relation with lesions of 

 the nervous system, whether these lesions im- 

 plicate the cerebro-spinal system, or the system 

 of the great sympathetic. 



We necessarily confine ourselves, in alluding 

 to these admirable researches, to the most 

 general results, and the conclusions flowing 

 most immediately from the experiments insti- 

 tuted. We reserve a more particular mention 

 of them for the proper place, namely, the 

 article on RESPIRATION, to which we beg to 

 refer. With regard to the opinions of writers 

 generally, we shall be content to observe here, 

 that they have for the most part regarded the 

 single physiological condition which was the 

 subject of their particular study as the only 

 source of animal heat. The general result of 

 their united labours, however, is, that there 

 are two principal sources, the one depending 

 on the arterial blood, the other on the energy 

 of the nervous system, a conclusion to which 

 we have come by another way, by combining 

 all the known facts that bear upon animal heat, 

 and embracing the manifestations presented by 

 the whole of the animal kingdom as well as 

 the isolated phenomena exhibited by man, and 

 this not in one but in every condition of ex- 

 istence, not only in the state of health but of 

 disease likewise, not as beings independent of 

 all things around them, but as living in intimate 

 relationship with external agents. 



OF THE PHYSICAL CAUSE OF AN IMAL HEAT, 



With regard to the physical cause of animal 

 heat, or to its mode of production, there was 

 a time, which we have not yet left very far 

 behind us, when natural philosophers and 

 chemists imagined they possessed the secret, 

 especially with reference to the mineral king- 

 dom. They have now discovered their mis- 

 take; and as the evolution of heat is a mystery 

 to them, it is not to be expected that it is less 

 so to physiologists, as manifested in the do- 

 main which they cultivate in peculiar. The 

 problem, in fact, becomes immensely com- 

 plicated by a variety of phenomena when from 

 the inorganic we ascend to the organic world. 

 All that could be done has been accomplished ; 

 from the particular conditions of organization 

 and of function upon which this effect 

 seemed to depend, physiologists have risen to 

 those that were the most general and com- 

 prehensive. This, in fact, was the end we 

 proposed in commencing this article. That 

 nothing may be omitted which can make the 

 sketch more complete, and none of the great 

 inquiries which have had animal heat for their 

 object may be passed over in silence, we shall 

 briefly cite the more important of those in 

 which the mode of production of animal heat 

 is discussed, always reserving to ourselves the 



