1M AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



heat-production increases with an increase of external temperature, because 

 with the rise of the latter bodily temperature increases, which in turn increases 

 metabolic activity (pp. 4:52, 433). ( lonsequently, in warm-blooded animals heat- 

 production is greater in cold climates and seasons than in the opposite conditions, 

 while in cold-blooded animals the opposite is the case. Cold applied to the skin 

 increases heat-production by reflex ly exciting muscular activity (shivering, etc., 

 p. 433) ; moderate heat exerts the opposite influence unless the bodily tem- 

 perature is affected, as shown by the results of studies of respiration (p. 433). 



The character of the food is important. Danilewsky 1 has estimated that the 

 following quantities of heat are produced under different diets, etc. : 



On a minimum diet 1800 kilogramdegrees. 



On a reduced diet (absolute rest) 1989 



On a non-nitrogenous diet 2480 " 



On a mixed diet (moderate work) 3210 " 



On an abundant diet (hard work) 3646 " 



On an abundant diet (very laborious work) 3780 



The influence of the quantity and quality of the diet must be potent when 

 it is remembered that 1 gram of proteid yields about 4100 calories, 1 gram of 

 fat about 9312 calories, and 1 gram of carbohydrate about 4116 calories. In 

 cold climates fats enter very largely into the diet because of the greater loss 

 of heat and the consequent increased demand for heat-producing substances. 



During the periods of digestion more heat is produced than during the in- 

 tervals, this increase being due chiefly to the muscular activity of the intestinal 

 walls (p. 431). Langlois' experiments indicate that during digestion heat- 

 production may be increased 35 to 45 per cent. 



It is said that heat-production undergoes diurnal variations which corre- 

 spond with the fluctuations of bodily temperature, but this is doubtful. 



All structures produce more heat during activity than during rest. Heat- 

 production has been estimated to be from two and a half to three times greater 

 when awake and resting than when asleep, and from one and a half to three 

 times more when active than when at rest, in proportion to the degree of 

 activity. During hybernation the absorption of O falls considerably (p. 434), 

 consequently heat-production is believed to decline to a like degree. 



All conditions which affect heat-dissipation (p. 494) tend indirectly to 

 influence heat-production. 



The most important of the factors influencing heat-production is the ner- 

 vous mechanism which controls the heat-producing processes (p. 490). 



Various dnu/s exert more or less potent influences directly or indirectly upon 

 heat-production. Cocain, strychnin, brucin, and other motor excitants increase 

 heat-production; while chloroform, most antipyretics, narcotics generally, bro- 

 mides, and motor depressants decrease heat-production. 



I bat-production is diminished in most forms of anaemia, after severe hem- 

 orrhage, and in most non-febrile adynamic conditions. It is usually increased 

 in fevers, especially so in infectious fevers. According to Liebermeister, the 

 1 Pflugei>s Arehivfur Physiologk, 1883, Bd. xxx. S. 190. 



