670 



ANIMAL HEAT. 



tion in the manner which has been indicated. 

 In summer we may presume, nay we may be 

 certain, that the differences obtain in degree 

 according to the mean intensity of the heat 

 proper to each. This is even to be proved by 

 direct experiment. The month of August, as 

 commonly happens, was not so hot as the 

 month of July, and six sparrows treated in the 

 same manner as those that were the subject of 

 the July experiment already detailed, were 

 found not to suffer refrigeration to the same 

 extent. After the lapse of an hour the mean 

 temperature of the six had sunk 1, 62, and 

 after three hours 4, 87 c., from which it is ob- 

 vious that with the successive declensions of the 

 external temperature the faculty of engendering 

 heat increases. This is demonstrated by the 

 experiments quoted. The animals that were 

 the subjects employed suffered a relatively less 

 degree of refrigeration in the cooler month than 

 they had done in the hotter, when exposed to 

 the same measure of cold. In the first set of 

 experiments performed in one of the coldest 

 months of the year, the power of resisting cold 

 was made particularly manifest. The sparrows, 

 kept for three hours in an atmosphere at the 

 temperature at which ice melts, scarcely suffered 

 any loss of heat at all. The results of the 

 three series of experiments detailed confirm, in 

 every particular, the conclusions which had 

 been come to analogically and a priori. They 

 do more than this. They bear out equally the 

 principles which had been deduced with refe- 

 rence to the constitutions more or less favoura- 

 ble to the production of heat. It is apparent, 

 in the first place, that the influence of the 

 summer and that of the winter act on the con- 

 stitution in the same manner as the two opposed 

 periods of early youth and adult age. Let us 

 therefore inquire in what manner these different 

 conditions tend to produce analogous effects. 

 We have seen that the constitution of early life 

 differed from that of adult age, especially in 

 the inferior energy of the functions of innerva- 

 tion and nutrition. Now this is that which 

 constitutes or causes the principal difference 

 between the winter and summer constitution of 

 man. We generally feel ourselves weaker in 

 summer than in winter, and our digestive 

 powers are then also decidedly less vigorous. 

 What completes the analogy is that the motions 

 of circulation and respiration are accelerated in 

 summer; and as a complement of the whole 

 of these data, the temperature is somewhat 

 higher in summer ; just as we have seen 

 that there is an epoch in youth when the tem- 

 perature exceeds that which is proper to com- 

 plete manhood. Thus, the parity between 

 the constitution of youth (in the second period 

 of childhood,) and that of the body in sum- 

 mer, contrasted with the constitution of the 

 adult age and that of the body in winter, exists 

 in the three following relations : 1st, a lessened 

 faculty of producing heat ; 2d, greater activity 

 in the motions of circulation and respiration ; 

 3d, a higher temperature of the body. 



But this faculty of adaptation to the different 

 seasons inherent in the body is only observed 

 in the better constitutions. That it may be 



manifested, it is necessary there be present a 

 certain energy of the nervous system ; without 

 this even the moderate colds of winter will not 

 be resisted. Without this the adult will have 

 a constitution that will present analogies with 

 that of early infancy. At present we merely 

 mention the kind of constitution ; we shall 

 return to the subjectby-and-by. 



Differences according to the nature of the 

 climate. The preceding facts render direct ex- 

 periments to ascertain the influence of the tem- 

 perature of different climates on the calorific 

 power altogether unnecessary. This is so far 

 fortunate ; for it were no easy matter to institute 

 them to the extent and with the precautions 

 necessary to security and satisfaction. The 

 knowledge of these effects is a necessary con- 

 sequence of the researches that precede. The 

 temperature of warm climates is represented by 

 the summer temperature of temperate climates, 

 with this difference, that it is higher, and that 

 with slight variations it continues through the 

 whole year. Whence it follows that warm 

 climates taken generally must produce effects 

 upon the constitution analogous to those pro- 

 duced by summer with us, only of greater 

 intensity by reason of the higher thermometric 

 range and longer continuance of the heat. The 

 inhabitants of hot climates ought consequently 

 to have an inferior degree of calorific power 

 than those of temperate or cold countries, what- 

 ever be the season. And we find, in fact, that 

 the natives of the warmer latitudes of the earth 

 present the characters in general that distinguish 

 the constitution of the body in the summers of 

 temperate countries, and characterizes the second 

 period of youth more rapid motions of the 

 circulatory and respiratory systems, and a 

 higher temperature, conjoined with an inferior 

 degree of energy in the functions of innervation 

 and nutrition. 



We shall not here enter upon the examina- 

 tion of the effects upon the natives of these 

 warmer latitudes from change of climate. We 

 shall speak of this elsewhere. After the periodi- 

 cal changes depending on the seasons we shall 

 pass to others of shorter duration, but which 

 revert much more frequently, and are under the 

 influence of other causes. 



INFLUENCE OF SLEEP ON THE PRODUCTION 

 OF HEAT. 



In the course of the twenty-four hours the 

 body is in two very different and in some sort 

 opposite states the states of sleeping and 

 watching. These two states are principally 

 contrasted in the energy and weakness of the 

 nervous system: from a perfect consciousness 

 of all that is passing, we suddenly observe a 

 complete suspension of this office in the whole 

 circle of the functions of relation. At the same 

 time the motions of the circulatory and respira- 

 tory system become slower. No more is needed 

 to lead to the conclusion that in this state the 

 temperature must be lower ; this is an inference 

 we draw without risk of error. But the degree 

 in which these motions are retarded is ex- 

 tremely limited ; and the depression of tem- 

 perature must be expected to be in the same 



