ANIMAL HEAT. <20[) 



The facts now, as well as those formerly adduced, go far Thetempera- 

 towards proving, that the temperature of warm-blooded ani- [J re J d war -™ 

 mals is considerably under the influence of the nervous system -, malsis con- 

 but what is the nature of the connection between them ? siderabiyinfk- 

 whether is the brain directly or indirectly necessary to the nervous 

 production of heat ? these are questions to which no answers »y»tem j 

 can be given, except such as are purely hypothetical. At 

 present we must be content with the knowledge of the insulated 

 fact : future observations may, perhaps, enable us to refer it to 

 some more general principle. 



We have evidence, that, when the brain ceases to exercise but the heat is, 



its functions, although those of the heart and lungs continue neverthel f 89 » 



° ° connected 



to be performed, the animal loses the power of generating with respira- 



heat. It would, however, be absurd to argue from this fact, tl0a - 



that the chemical changes of the blood in the lungs are in no 



way necessary to the production of heat, since we know of no 



instance in which it continues to take place after respiration has 



ceased. 



It must be owned, that this part of physiology still presents 

 an ample field for investigation. 



Of opinions sanctioned by the names of Black, Laplace, 

 Lavoisier, and Crawford, it is proper to speak with caution 

 and respect, but without trespassing on these feelings, I may 

 be allowed to say, that it does not appear to me that any of 

 the theories hitherto proposed afford a very satisfactory expla- 

 nation of the source of animal heat. 



Where so many and such various chemical processes are Can any one 

 going on, as in the living body, are we justified in selecting any chen J» cal P r °- 

 one of these for the purpose of explaining the production of e d as the cause 

 heat ? of the heat ? 



To the original theory of Dr. Black, there is this unan- 

 swerable objection, that the temperature of the lungs is uot 

 greater than that of the rest of the system. To this objection, 

 the ingenious and beautiful theory of Dr. Crawford is not 

 open - } but still it is founded on the same basis with that of 



Dr. 



of the lungs is either extremely impaired, or altogether destroyed, so 

 that the animal does not feel ttie same desire to draw in fresh air : in 

 consequence his inspirations hecome less frequent than natural, and 

 hence arise the phenomena produced by this operation. 



