388 PHILOSOPHY OF ZOOLOGY^ 



But admitting the principles on which the opinions of 

 BLACK and CRAWFORD rest, it will be seen, from the condi- 

 tions of the problem which have been stated, that they of- 

 fer no explanation of many of the changes which occur. 

 Nay, it may be affirmed with confidence, that the support- 

 ers of these opinions have not put themselves to any 

 trouble in order to obtain a knowledge of these conditions, 

 but have suffered themselves to be seduced by the expla- 

 nation they seemed to afford of some of the phenomena. 

 In consequence of this neglect, a theory which was long the 

 boast of the chemist, has been rejected as visionary ; and 

 the disappointed physiologist is now left to re-examine the 

 properties of that vital principle he had inconsiderately 

 abandoned. 



In the present state of physiological science, no rational 

 theory can be offered to account for the production and 

 regulation of animal heat. Perhaps the changes which take 

 place in the fluids of animals may occasion a disengage- 

 ment of heat or cold, in consequence of the difference in 

 their capacities. But a variety of other circumstances ap- 

 pear to operate. The compression of the air in the lungs in 

 the act of breathing, and the compression of the blood, by the 

 muscular power of the heart and arteries, may likewise ex- 

 ercise some influence. We are inclined to believe, however, 

 that the principal source of animal heat may with propriety 

 be referred to the electrical changes which accompany those 

 endless combinations and decompositions which take place 

 in the system through the whole of life, changes which are 

 necessary to the wellbeing of the principle of life, and de- 

 monstrated to be subject to its control. 



