446 NUTRITION ANIMAL HEAT AND FORCE. 



with those obtained by the indirect methods, 2'5 heat-units per pound per 

 hour (1-39 kilo.-degree 0. per kilo.), it is seen that the indirect estimates 

 give about 37 per cent, less heat produced than is given by direct estimates. 

 It is on account of this great difference, that writers are at a loss to give 

 definite estimates of the actual quantity of heat produced by the body. 



A study of this subject and of the details of observations both direct 

 and indirect has made it evident that the experimental difficulties to be 

 overcome and the unavoidable elements of inaccuracy are greater in the 

 direct than in the indirect method. In comparing the estimates of heat 

 actually produced with the heat value of food which, of course, is the ulti- 

 mate source of heat and force in the body the correspondence is much 

 closer if the indirect estimates be adopted. It therefore seems more in ac- 

 cordance with ascertained facts to adopt the indirect estimates, although this 

 can not be done without reserve. The heat produced, then, is probably 

 equal to about 2'5 heat-units (pound-degrees) per hour per pound weight of 

 the body (nearly 1-4 kilo.-degree 0. per kilo.) This is equal to about 8,400 

 heat-units, or about 2,120 kilo.-degrees C., in twenty-four hours ; which is 

 equal to about 6,500,000 foot-pounds, or about 900,000 kilogrammetres. 



The normal variations in the production of heat are not absolutely and 

 definitely represented by variations in the actual temperature of the body 

 and by the consumption of oxygen. Muscular work may increase the pro- 

 duction of heat 60 per % cent. (Hirn) while it increases the consumption of 

 oxygen about 4^ times, a large part of the oxidation being expended in the 

 form of work. The production of heat is diminished in fasting animals 

 (dogs) by nearly 45 per cent. (Senator), after deprivation of food for two 

 days. In old age and in infancy, there is less heat produced than in adult 

 life. The production of heat is less in females than in males and is less dur- 

 ing the night than during the day. These points will be touched upon again 

 in connection with the normal variations in the temperature of the body. 



Limits of Variation in the Normal Temperature in Man. One of the 

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

 duce a registering thermometer into the axilla, reading off the degrees after 

 the mercury has become absolutely stationary. N early 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 temper- 

 ate climate, ranges between 97*7 and 99-5 Fahr. (36-5 and 37'5 C.). Davy, 

 from a large number of observations upon the temperature under the tongue, 

 fixed the standard, in a temperate climate, at 98 Fahr. (36-67 0.) The 

 axilla and the tongue, however, being more or less exposed to external influ- 

 ences, 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 in pathological examinations. As a standard for compari- 

 son, it may be assumed that the most common temperature in these situa- 

 tions is 98 Fahr. (36'67 C.) subject to variations, within the limits of 

 health of about 0-5 Fahr. (0-27 C.) below and 1-5 (0-82 Fahr. C.) above. 



Variations with External Temperature. The general temperature of the 



