ANIMAL HEAT. 511 



actual temperature of the body is not notably reduced, the power of resisting refrigerat- 

 ing influences is diminished very considerably. 



There are no positive observations showing any constant differences in the tempera- 

 ture of the body in the sexes ; and it may be assumed that, in the female, the animal 

 heat is modified by the same influences and in the same way as in the male. 



Diurnal Variations in the Temperature of the Body. Although the limits of variation 

 in the animal temperature are not very extended, certain fluctuations are observed, 

 depending upon repose or activity, digestion, sleep, etc., which it is necessary to take 

 into account. These conditions, which are of a perfectly normal character, may in- 

 duce changes in the temperature amounting to from one to three degrees. It has been 

 ascertained that there are two well-marked periods in the day when the heat is at its 

 maximum. These, according to the most recent observations in Germany, are at eleven 

 A. M. and four p. M. ; and it is a curious fact, that, while all observations agree upon this 

 point, the very elaborate experiments of Lichtenfels and Frohlich show that these periods 

 are well marked, even when no food is taken. Biirensprung and Ladame farther show 

 that the fall in temperature during the night takes place sleeping or waking ; and that 

 when sleep is taken during the day it does not disturb the period of the maximum, which 

 occurs at about four p. M. According to these experiments, at eleven in the morning, 

 the animal heat is at one of its periods of maximum ; it gradually diminishes for two or 

 three hours and is raised again to the maximum at about four in the afternoon, when it 

 again undergoes diminution until the next morning. The variations amount to from about 

 1 to 2'16. The minimum is always during the night. 



The relations of the animal temperature to digestion are still somewhat indefinite. It 

 is well known that activity of the digestive organs increases the consumption of oxygen, 

 and, to a corresponding degree, the exhalation of carbonic acid ; but we have to assume 

 that the production of heat is in direct ratio to the respiratory action in order to estab- 

 lish any relation between calorification and the digestion of ordinary food. It is easy to 

 calculate that a given amount of oxygen will produce a definite quantity of carbonic acid, 

 and will, by its union with carbon and hydrogen, generate a certain number of "units 

 of caloric ; " but the mechanism of the production of animal heat is too complex and not 

 well enough understood to admit of such positive reasoning. There is, indeed, no experi- 

 mental evidence of any marked and constant change in the general temperature of the 

 body during the ordinary process of digestion ; but it is none the less true that the quan- 

 tity and quality of food bear a certain relation to calorification. This is inevitable from 

 the connection of animal heat with the general process of nutrition ; but this relation is 

 expressed in the connection of calorification with nutrition of the tissues, and not in the 

 process of the digestion or absorption of food. We shall see that, when nutrition is modi- 

 fied by alimentation, the general temperature is always more or less affected ; and when 

 the requirements of the system, as far as the generation of heat is concerned, are 

 changed, by climate or otherwise, alimentation is modified. One of the objects of ali- 

 mentation and nutrition is to maintain the body at a nearly constant temperature. 



The influence of defective nutrition or inanition upon the heat of the body is very 

 marked. John Hunter, in his experiments upon animal heat, made a few observations 

 upon this point and noted a decided fall in temperature in a mouse kept fasting. The 

 same phenomena were also observed by Collard de Martigny ; and Chossat noted the 

 effects of deprivation of food upon the power of maintaining the animal temperature, in 

 the most exact and satisfactory manner. In pigeons, the extreme diurnal variation in 

 temperature, under normal conditions, was found by Chossat to be 1'3. During the 

 progress of inanition, the daily variation was increased to 5 -9, with a slight but well- 

 marked diminution in the absolute temperature ; and the periods of minimum tempera- 

 ture were unusually prolonged. Immediately preceding death from starvation, the dimi- 

 nution in temperature became very rapid, the rate, in the observations on turtle-doves, 



