ANIMAL HEAT. 



6M 



of warm-blooded animals, then, are four in 

 number, three of which are referable to the 

 organs of nutrition, the fourth to the nervous 

 system, which may be briefly related in the 

 following order: 1. higher complication and 

 greater extent of the digestive apparatus; 2. 

 entire separation of the circulating apparatus 

 into two systems, the venous and arterial, with- 

 out direct communication between them ; 3. 

 organs of aerial respiration presenting a much 

 larger surface to the contact of the atmosphe- 

 rical air ; 4. a nervous system of which the 

 axis, and especially the encephalic extremity, 

 bears a very high ratio to the whole. 



These structural characters determine the 

 following modifications of function. 1st, 

 The complexness and greater extent of the di- 

 gestive apparatus in warm-blooded animals 

 produces a more perfect elaboration of the 

 matters which serve for the formation of blood. 

 2nd, The arrangement of the parts of the cir- 

 culating system maintains the arterial blood 

 quite distinct from the venous, and in a state 

 of complete purity. 3rd, The respiratory ap- 

 paratus, by the great extent of its surfaces in 

 contact with the air, secures that its distinguish- 

 ing qualities be imparted in the highest pos- 

 sible degree to the arterial blood, which more- 

 over is elaborated in larger quantity. The 

 predominance of their nervous system, and es- 

 pecially of its encephalic extremity, renders 

 all the parts of the body much more excitable, 

 and gives the greatest energy to the nutritive 

 functions. The whole of these organic condi- 

 tions are mutually dependent, and may be 

 reduced to the expression of these two general 

 conditions: 1st, the formation and distri- 

 bution of the arterial blood, the particularly 

 exciting find nutritive blood of the body ; 2nd, 

 the most powerful influence of the nervous 

 system. 



As these characters of primary significance 

 in the animal economy coincide in Mammalia 

 and Birds with the greater production of heat, 

 and thus distinguish them from all other ani- 

 mals, it is probable that between these organic 

 conditions and caloricity or the power of 

 evolving caloric, there is a relation of the na- 

 ture of cause and effect. It is even almost 

 impossible that this should be otherwise than 

 as it has been stated ; for the characters of 

 organization and the peculiarities of function, 

 coincident with the greater evolution of calorie, 

 are almost the sole points of any importance 

 that distinguish warm from cold-blooded ani- 

 mals. 



It is therefore nearly certain that the condi- 

 tions requisite to the production of heat must 

 exist within the circle of the functions which 

 we have described. And if this relation do 

 actually exist as these functions are in a 

 state of mutual dependence, it follows that 

 one of them cannot be modified, the others 

 remaining, so to speak, in the same condition, 

 without modification resulting in the calorific 

 capacity likewise. It is of great consequence 

 to verify this assumption, because if it be 

 well-founded, the probability already elicited 

 of the power of engendering heat being de- 



pendent on the state of the functions in the 

 relations which have been indicated, becomes 

 matter of certainty. So that it is of the highest 

 import to follow the modifications of these 

 functions presented by animals and man in 

 order to compare them with the respective 

 varieties of calorific power presented by each. 

 And if we find that they coincide, and accord 

 with the principle established, we shall have 

 discovered the conditions of organization and 

 of function upon which the production of ca- 

 loric depends. 



Conditions of organization and of func- 

 tions may be entitled the physiological causes 

 of the production of animal heat. If we 

 succeed in determining these, we ought to 

 rest satisfied. If, indeed, to this knowledge 

 we could add that of the immediate cause of 

 this phenomenon among animals, or what is 

 the physical cause, it would be a great gain 

 for science. This, accordingly, was the ob- 

 ject of the labours of the majority of phy- 

 siologists who have given their attention to the 

 subject of animal heat. But they could not possi- 

 bly succeed in their researches, for the simple 

 reason that natural philosophers themselves have 

 not yet discovered how heat is produced in the 

 inorganic world ; although indeed they have 



Presumed that they were acquainted with it. 

 t is not to be wondered at, then, that attempts 

 have been made to detect this presumed cause 

 amidst the complicated phenomena of life. 

 But natural philosophers have lost confidence 

 in the theory which they had formed, and are 

 searching for a new one. Meantime they are 

 doing what ought always to be done under 

 such circumstances ; they are studying with 

 care the various conditions and circumstances 

 in which it is produced ; determining these 

 with precision, and measuring with rigour the 

 quantity of heat produced. Of late, therefore, 

 many distinguished physiologists have entered 

 on the same path, and by experiment have 

 endeavoured to ascertain the physiological con- 

 ditions of the production of heat. But if 

 their predecessors have not attained the object 

 they had in view, they have nevertheless ren- 

 dered very essential services to science ; for in 

 searching after the physical cause of heat, they 

 have determined with precision the physiological 

 conditions of the production of animal heat, 

 which are of very great importance. Inde- 

 pendently of the simple observation of the actual 

 temperature of animals, the labours of physio- 

 logists on this subject consist almost entirely 

 of experimental facts, that is to say, facts 

 created by science. 



But there is one source of inquiry into the 

 laws of animal heat which has been little 

 dipped into, although it is beyond all comparison 

 the most abundant. I allude to that presented 

 to us by nature in the all but infinite variety 

 of modifications of organization and pheno- 

 mena exhibited in the vast chain of animated 

 things, not only in the diversities of species, 

 but also in the varieties of age and constitution, 

 and the changes induced by the states of health 

 and disease. In making this an object of 

 peculiar study, we become acquainted with 



