ANIMAL HEAT. 507 



ature when exposed to cold, or of moderating it when exposed to heat, death is the invari- 

 able result. 



The production of animal heat is so closely connected with nutrition, that, in serious 

 pathological modifications of this process, as in the essential fevers or extensive inflam- 

 mations, the temperature of the body becomes an Important guide, particularly in 

 prognosis. 



The study of the temperature in different classes of animals presents very great inter- 

 est, but the limits of a work on pure human physiology restrict us to the phenomena as 

 observed in man, and in animals in which the processes of nutrition are similar, if not 

 identical. We shall therefore treat of the subject from one point of view and consider 

 it as follows : 



1. The normal temperature in the human subject, with its variations in different parts 

 of the body and at different periods of life. 



2. The diurnal variations in the animal temperature, and the relations of alimenta- 

 tion, digestion, respiration, nutrition, exercise, and the nervous system. 



3. The means by which the temperature of the body is kept within the limits neces- 

 sary to the preservation of life and health. 



Limits of Variation in the Normal Temperature in Man. A great number of obser- 

 vations have been made upon the normal temperature in the human subject under differ- 

 ent conditions ; but we shall cite those only in which all sources of error in thermometry 

 seem to have been avoided, and in which the results present noticeable peculiarities. 

 One of 'the most common methods of taking the general temperature has been to intro- 

 duce a delicate thermometer, carefully protected from all disturbing conditions, into the 

 axilla, reading off the degrees after the mercury has become absolutely stationary. 

 Nearly all observations made in this way agree with the results obtained by Gavarret, 

 who estimated that the temperature in the axilla, in a perfectly healthy adult man. in a 

 temperate climate, ranges between 97*7 and 99*5 Fahr. Dr. Davy, from a large num- 

 ber of observations upon the temperature under the tongue, fixes the standard, in a 

 temperate climate, at 98. When we examine the temperature of the blood in the deeper 

 vessels and the variations in different parts, we shall see that the axilla and the tongue, 

 being more or less exposed to external influences, do not exactly represent the general 

 heat of the organism ; but these are the situations, particularly the axilla, in which the 

 temperature is most frequently taken, both in physiological and pathological examina- 

 tions. As a standard for comparison, we may assume that the most common temperature 

 in these situations is 98, subject to variations, within the limits of health, of about 0'5 

 below and 1-5 above. 



Variations with External Temperature. There can be no doubt that the general tem- 

 perature of the body varies, though within very restricted limits, with extreme changes 

 in climate. The results obtained by Davy, in a large number of observations in temper- 

 ate and hot climates, show an elevation in the tropics of from 0'5 to 3. It is well 

 known, also, that the human body, the surface being properly protected, is capable of 

 enduring for some minutes a heat much greater than that of boiling water. Under these 

 conditions, the general temperature is raised but very slightly, as compared with the 

 intense heat of the surrounding atmosphere. According to the observations of Dr. Dob- 

 son, the temperature was only raised to 99'5 in one instance, 101'5 in another, and 102 

 in a third, when the body was exposed to a heat of more than 212. MM. Delaroche 

 and Berger, however, found that the temperature in the mouth could be increased by 

 from 3 to 9, after sixteen minutes' exposure to intense heat. This was for the external 

 parts only ; but it is not at all probable that the temperature of the internal organs ever 

 undergoes such extensive variations. 



It is very difficult to estimate the temperature in persons exposed to intense cold, as 



