CHAPTER LI. 



IKE PRODUCTION OF HEAT IN THE BODY— ITS MEAS- 

 UREMENT AND REGULATION— BODY TEMPERA- 

 TURE— CALORIMETRY— PHYSIOLOGICAL 

 OXIDATIONS. 



It is customary to date our modern ideas of the origin of 

 animal heat from the time of Lavoisier (1774-77). To the older 

 physiologists it was a most difficult problem. The animal's body 

 produces heat continually and maintains a temperature higher, as 

 a rule, than that of the surrounding air. Since oxygen and the 

 nature of ordinary combustions were unknown, they naturally 

 explained this heat formation by reference to causes which the 

 science of the day had shown to be capable of producing warmth, 

 such as friction and fermentation. Haller (1757), for instance, 

 taught that the body heat arises mainly from the friction of the 

 circulating blood and the movements of the heart and blood-vessels, 

 and this view found currency in text-books well into the nine- 

 teenth century. Lavoisier first gave to the physiologist the con- 

 ception that the heat produced in the body is due to a combustion or 

 oxidation, and that therein lies the significance of our respiration 

 of oxygen. He believed himself that this oxidation takes place in 

 the lungs, — that is, the blood brings to the lungs a hydrocarbon- 

 ous material which is attacked by the oxygen and burnt with 

 the formation of water and carbon dioxid and the liberation of 

 heat. Later experimenters demonstrated that the heat production 

 does not occur in the lungs, at least not exclusively, but over the 

 whole of the body. After a long and interesting controversy it was 

 also shown satisfactorily that the oxidations of the body do not 

 occur in the blood, but in the tissues themselves. The oxygen is 

 transported to the cells and there does its work of effecting oxi- 

 dations and giving rise to heat. This heat is equalized more or 

 less over the whole body, chiefly by the circulation of the blood, 

 which absorbs heat from the warmer organs and distributes it to 

 the cooler ones. The body temperature is maintained at a nearly 

 constant level by an intricate adjustment of physiological reflexes 

 which together constitute the heat-regulating mechanism. Such 

 in brief is the general theory of our time regarding heat production 

 in the body. Many of the problems that interested the older phys- 



