THE PRODUCTION AND DISSIPATION OF HEAT 1099 



person who restricts his diet to carbohydrates in summer and to meat 

 and fat in winter unconsciously proves that the heat of combustion of 

 the former is low and that of the latter high. This fact is illustrated 

 further by the differences in the character of the food of the inhabitants 

 of the northern and southern countries, the oily and fatty food of the 

 far north being relished mainly on account of its high heat value. The 

 influence of muscular contraction is elucidated further by the fact 

 that very high temperatures are frequently encountered in tetanus 

 and the status epilepticus. In addition, MacCullum^ states that high 

 temperatures are always noted in dogs when suffering from spasms 

 following parathyroidectomy. Moreover, since these convulsions 

 may be stopped by the administration of calcium acetate, this salt 

 likewise reduces their body-temperature. These and other phe- 

 nomena which might still be mentioned, show very clearly that the 

 production of heat is controlled by involuntary and voluntary im- 

 pulses involving the different tissues, chiefly the muscles. ■ 



Heat-dissipation. Thermolysis. — An animal loses its heat in 

 two ways, namely, by radiation or conduction from its skin and mucous 

 surfaces, and in the form of bound or latent heat in its different fluid 

 and semi-solid excreta. The channels which take part in this dissipa- 

 tion are the skin, pulmonary tract, alimentary canal and urinary 

 passage. From the skin heat is lost by radiation, conduction and con- 

 vection as well as in the form of bound heat in its secretions, the sweat 

 and sebaceous material. The pulmonary passage transfers heat to the 

 inspired air both directly as well as in the watery particles which are 

 added to the expiratory air. The alimentary canal discharges a 

 certain amount of heat in the feces and also imparts some of it to the 

 food when taken into the mouth and stomach. Obviously, the tem- 

 perature of the latter must be raised to that of the bodyi The urinary 

 tract gives off a certain amount of latent heat in the urine. 



Under ordinary conditions by far the greatest loss of heat occurs 

 through the skin and its appendages. Furthermore, since the inten- 

 sity of radiation depends upon the nature of the surface as well as upon 

 the excess of temperature of the radiating surface over that of the sur- 

 rounding medium, it will be evident that the uncovered areas of the 

 skin must discharge a greater amount of heat than those protected 

 by hairs or clothing. In addition, it is to be noted that the more 

 vascular regions, such as the forehead, radiate more heat than the less 

 vascular ones, such as the lobules of the ears or the tip of the nose. 

 In either case, however, the loss of heat may be increased by moving 

 about or by setting up currents in the surrounding air, because these 

 procedures tend to augment the difference in the temperatures of the 

 radiating surface and the absorbing medium. 



In measuring the radiating heat we make use of an instrument 

 which is constructed after the principle of the resistance thermometer 

 and is known as the resistance radiometer or bolometer. It consists of 



1 Harvey Lectures, New York, 1908-09. 



