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i.v AMERICAN TEXT-BOOK OF PlfYSIOLOd V. 



that tend to excite the animal. Tin- chief sources of error in the calorime- 

 try are in failures to obtain accurate temperatures of the calorimeter and of 

 the animal. In the latterea.se inaccuracy is to some extent absolutely una- 

 voidable, chiefly because of normal fluctuations which occur frequently and are 

 often very marked. 



Conditions affecting- Heat -production. — The quantity of heat produced 

 must necessarily vary with many circumstances. Estimates of heat-production 

 in the adult range in round numbers from 2000 to 3000 kilogramdegrees per 

 diem according to the method and incidental circumstances. Thus, according 

 to— 



vScliarling 3169 kilogramdegrees 



Vogel 2400 " 



Him 3725 " 



Leyden 2160 " 



Hemholtz 2732 " 



Rosenthal 2446 " 



Danilesky 3210 « 



Ludwig 3192 " 



Ranke 2272 kilogramdegrees 



Kiibner 2843 " 



Ott 103 '• 



per hour during the afternoon (weight of 



man 87.3 kilograms). 

 Lichatschew .... 33.072 to 38.723 kilo- 



gramdegrees per kilogram of body-weigh! 



per diem. 1 



The chief conditions which affect heat-production are age, sex, constitution, 

 body-weight and body surface, species, respiratory activity, the condition of 

 the circulation, internal and external temperature, food, digestion, time of day, 

 muscular activity, the activity of heat-dissipation, nervous influences, drugs, 

 abnormal and pathological conditions. 



Young animals produce more heat, weight for weight, than the mature. This 

 is owing chiefly to the greater activity of the metabolic processes in the former, 

 and in part to the relatively larger body surface, young animals generally 

 being smaller than the matured and thus having, in proportion to body-weight, 

 larger radiating surfaces. 



Heat-production is more active in the robust than in the weak, other con- 

 ditions being the same. 



The weight of the body is obviously a most important factor in relation to 

 the quantity of heat produced, especially as regards the weight of the active 

 tissues in relation to inactive structures such as bone, sinew, and cartilage. 

 Two animals of the same weight may produce very different quantities of 

 heat per diem, other things being equal. Thus, a fleshy animal should 

 naturally be expected to produce more heat than one with very little flesh and 

 an abundance of fat, which is an inactive heat-producing structure. While, 

 therefore, the relation of heat-production to body-weight does not seem to be 

 definite, yet the experiments by Reichert 2 and by Carter 3 indicate that heat- 

 production bears, broadly speaking, a direct relation to body-weight. 



Heat-production is greater relatively in homothermous than in poikibther- 



1 The figures by ott {New York Medical Journal, 1889, vol. 16, p. 29) and Lichatschew 



inauguralis, St. Petersburg, 1893; quoted in Hermann's Jahresberichte der Physioloyie, 

 3. 99) were obtained by means of a water calorimeter. 



2 University Medical Magazine, 1890, vol. '_', p. 225. 



3 Journal of Nervous and Mental Diseases, 1890, v>>\. 17, p. 782. 



