ANIMAL HEAT. 



667 



the temperature of ten children born at the full 

 time was 34,75 c. (94,5 F.) ; the tempera- 

 ture in no case descending lower than 34 

 (94 F.), and ranging between this and 35,5 c. 

 (96 F.). Let it be observed that at the 

 seventh month the membrana pupillaris no 

 longer exists ; the infant has, therefore, at this 

 epoch of its development, the essential charac- 

 ters of warm-blooded animals capable of sup- 

 porting a high temperature when that of the 

 surrounding atmosphere is mild. But if it 

 were entering the world some considerable time 

 before the disappearance of the pupillary mem- 

 brane, it would be in a condition analogous to 

 the Mammalia which are born with their eyes 

 shut ; it would no longer be in a condition to 

 maintain an elevated temperature, and without 

 doubt would lose heat precisely as they do 

 without precautions to the contrary. 



When we take a general view of the first and 

 second periods in the early life of warm-blooded 

 animals, we find that they are under the influence 

 of two general conditions relative to calorifica- 

 tion ; conditions which, acting inversely, tend 

 to compensate each other mutually ; on the 

 one hand, the celerity of the motions ; on the 

 other, the imperfection of the nutrient and ner- 

 vous functions. The celerity of the motions of 

 circulation and respiration diminishes, whilst 

 the development of the nutritive and nervous 

 functions increases with age. These two con- 

 ditions influencing the production of heat are, 

 therefore, in an inverse ratio to one another. 

 And according to the nature of these relations 

 will the temperature vary. Were the opposite 

 effects equal, there would be exact compensa- 

 tion in the whole phases of the evolution, from 

 the moment of birth to that of perfect adole- 

 scence, and the temperature of the body would 

 be the same at every period of life. But the 

 progression in the celerity of the movements on 

 the one hand and of corporeal development on 

 the other, is unequal ; and there is but a single 

 epoch in the whole course of childhood when 

 such an equality or balance exists, and at 

 which consequently the temperature of the 

 child is the same as that of the adult. Previous 

 to this epoch, the nutritive and nervous func- 

 tions are so imperfectly developed, that their 

 influence, inimical to the production of heat, 

 surpasses the favourable tendency to this end, 

 which we have in the celerity of the motions of 

 circulation and respiration. It follows that the 

 temperature of the body is inferior at the pre- 

 ceding limit or to that of the adult state ; with 

 the progress of time, however, the child attains 

 this limit, and then we have a new relation 

 established. The evolution of the nutritive and 

 nervous functions continues, and although it 

 have not yet attained its ultimate term, the de- 

 fect of heat which results from this is all but 

 compensated by the celerity of the motions, 

 which is still sufficiently great, to surpass in a 

 marked degree the celerity of the motions in 

 the adult. The temperature at this period will, 

 therefore, be above that of the adult. This pe- 

 riod lasts for several years in childhood or 

 youth ; but then comes a gradual retardation 

 in the motions both of respiration and circula- 



tion, and with this a reduction of the tempera- 

 ture to the standard of the adult. 



There are consequently four states of the 

 temperature from birth up to adolescence inclu- 

 sive. In the first period the temperature is at 

 the minimum ; in the second, it attains the 

 adult degree ; this might be entitled the period 

 of the mean temperature ; in the third, the 

 temperature exceeds that of the adult; finally, 

 in the fourth, it sinks to the mean, that is, 

 the temperature of the adult. 



There are, therefore, constitutions in the same 

 class of animals which are more or less favour- 

 able to the production of heat ; for it is so 

 among individuals that differ in age in the 

 limits between the moment of birth and 

 that at which adolescence is completed ; and 

 this leads us to new considerations. 



DIFFERENCES OF CONSTITUTION IN RELATION 

 WITH THE PRODUCTION OF HEAT AMONG 

 ANIMALS. 



Since the body and the functions are pro- 

 gressively developed, and without interruption 

 between the two grand periods named, there is 

 in the course of this long interval as much dif- 

 ference in the state of the constitution as there 

 are sensible degrees of development ; a circum- 

 stance that implies a long series of varieties. 

 But these intimate differences are not mani- 

 fested externally by corresponding states of 

 temperature of body. For we have seen that 

 this undergoes but four sensible variations in 

 this respect, and that, of these four modifications, 

 two were of like import. It is every way 

 worthy of attention to observe that, at the point 

 which separates the first from the second period 

 of infancy, the temperature should be equal to 

 that of the adult. 



It is difficult to imagine that this equality 

 can exist under every variety of external cir- 

 cumstance, when we see that the elements upon 

 which it depends are so different. And this 

 leads us to consider the production of heat 

 under a new point of view. Under what cir- 

 cumstances has this equality of temperature be- 

 tween the infant and the adult been observed ? 

 It was when the external temperature was mild 

 or even warm. Would the same thing have 

 been observed had this been cold or severe ? 

 It is evident that if the faculty to produce heat 

 is the same at this period of infancy as it is in 

 adult age, the heat of the body will always re- 

 main the same, making abstraction of the diffe- 

 rences that depend on those of simple corpo- 

 real bulk. Thus, all things else being equal, a 

 young animal at this epoch ought to cool to the 

 same degree as an adult under the influence of 

 external cold, if it have the same power of pro- 

 ducing heat. If, however, it be inferior in its 

 calorific powers, it will not be competent to 

 maintain its temperature to the same degree as 

 the adult, and it will fall under this limit in a 

 proportion determined by the difference which 

 exists in the faculty of producing heat. On 

 making application of the principles which 

 have been already announced, let us try if we 

 cannot predict the effects. By reason of the 

 inferiority in energy of the nervous system in 



