664 



ANIMAL HEAT. 



minutes more it fell 3, 12 ; in thirty minutes 

 more 2, 50 ; in twenty-five minutes more 

 1, 25; in thirty minutes morel , 25; so that 

 in the course of four hours in all the tempe- 

 rature declined by the amount of 18, 12 of 

 the centigrade scale (about 33 F.) ! Not only 

 had the temperature of the animal sunk by so 

 large a quantity in so short a period of time, 

 the external temperature being pleasant, but it 

 actually could maintain its temperature at no 

 higher a grade than 6, 75 c. (44, 5, F.) above 

 that of the atmosphere. Experiments of the same 

 kind performed on three other puppies of the 

 same litter presented results in all respects 

 analogous. The cooling may even go much 

 further by protracting the period during which 

 the young animals are kept apart from their 

 parent. For instance, four puppies, twenty- 

 four hours old and of much smaller size than 

 the subjects of the former experiments, after 

 having sunk 16 c. in four hours and thirty 

 minutes, lost six degrees more of temperature 

 in the succeeding eight hours and thirty mi- 

 nutes, the air remaining all the while at 13 c. 

 (53, 5 F.). They consequently lost twenty- 

 two degrees centigrade in thirteen hours ; and, 

 what is very remarkable, their final temperature 

 was but one degree above that of the surround- 

 ing air. Kittens and rabbits of the same age 

 exhibited similar phenomena, if possible in a 

 more striking degree. Some kittens were ob- 

 served to cool twenty degrees centigrade within 

 the short interval of three hours and a half, 

 and some young rabbits suffered the same de- 

 pression of temperature in two hours and ten 

 minutes, the air being at the time at 14 c. 

 (57, 5 F.), These phenomena are unques- 

 tionably among the most remarkable we wit- 

 ness in warm-blooded animals. For here we 

 have species of different genera of the Carni- 

 vora and Ilodentia, which at two periods of 

 their existence present the extremes in the pro- 

 duction of heat. They may be said to be, 

 to all intents and purposes, cold-blooded ani- 

 mals, with reference to temperature, during 

 the earliest period of life; they are only truly 

 warm-blooded animals in a later stage of their 

 existence. The same phenomena undoubtedly 

 present themselves in many other species ; but 

 it would not be reasonable to suppose that they 

 were exhibited by all. 



The phenomena being connected with the 

 state of constitution, it may be expected to 

 vary in different genera and families; and this, 

 in fact, is what actually happens. A young 

 guinea-pig, for instance, having a temperature 

 of 38 c. (101, 5 F.), will maintain this tem- 

 perature when the atmosphere is mild, although 

 separated from its mother. It is the same with 

 the goat. These instances are enough to give 

 us a key to the external characters in relation 

 with the different capacities to produce heat 

 inherent in the young Mammalia. In the first 

 place we observe a manifest relation with the 

 state of energy of the nervous system : on the 

 one hand we have the puppy, the kitten, the 

 rabbit, which are born extremely weak ; on the 

 other we have those animals that come into the 

 world in a condition to walk, to eat, and, as it 



were, furnished forth to a certain extent with 

 the means of providing for their wants. The 

 question, however, is to discover some zoolo- 

 gical character in relation with these differ- 

 ences. If this were to be derived from the 

 state of the organs of locomotion, of the faculty 

 of walking, we should sometimes be led into 

 error ; for man, at the period of his birth and 

 long afterwards, is not in a condition to hold 

 himself erect, and yet his temperature is main- 

 tained to within one or two degrees of that of 

 his mother, if the external temperature be but 

 mild. There is, however, one character that 

 appears general ; this is the state of the eyes. 

 2'hose species of Mammalia which in the earlier 

 period of their existence do not maintain their 

 temperature, that of the external atmosphere 

 being mild or warm, but cool down to the 

 standard of the cold-blooded animals, are born 

 with their eyes closed ; whilst those which main- 

 tain their temperature, that of the external 

 atmosphere being mild, are born with, their eyes 

 open ; and this, whether they can walk about 

 like the guinea-pig, the kid, &c., or cannot do 

 so, as is the case with the human infant in par- 

 ticular. 



This general view of the state of energy of the 

 nervous system in relation with the production 

 of heat in early life, comes in aid, in a very 

 remarkable manner, of the general principles 

 which have been already deduced in regard to 

 the calorific power. In going more deeply 

 into the subject, the confirmation becomes more 

 manifest and more complete. The state of the 

 eyes affords a mere external and zoological in- 

 dication. It is but an indication of other deep 

 modifications of the economy, which it is 

 essential to determine more closely. Now in 

 examining the state of the organs generally of 

 puppies at the period of their birth, we observe 

 a remarkable disposition of the sanguiferous 

 system. The ductus arteriosus continues per- 

 vious and of large size. The consequence of 

 this structure is that a free communication is 

 established between the arterial and venous 

 blood, by which they are mingled in large pro- 

 portion one with another. And here we have 

 precisely the physiological character derived 

 from the nature or quality of the blood which 

 distinguishes the cold-blooded from the warm- 

 blooded Vertebrata (in the adult age under- 

 stood). This character is exactly the same in 

 the other species of Mammalia which we have 

 mentioned as losing temperature and attaining 

 the standard of the cold-blooded tribes. On 

 the other hand, in the guinea-pig, to take an 

 individual instance, which from the first day of 

 its extra-uterine existence maintains its tempera- 

 ture nearly on a level with that of its parent 

 when the air is temperate, the ductus arteriosus 

 is closed immediately after birth. The arterial 

 remaining distinct from the venous blood, this 

 creature is therefore born with the organization 

 characteristic of warm-blooded animals, and 

 presents phenomena having reference to calori- 

 fication of the same kind as adult warm-blooded 

 animals. 



This relation is preserved in the young 

 Mammalia in every modification in a pecu- 



