880 SPECIAL PHYSIOLOGY. 



owing to quickening of the circulation, or, as some have supposed, by 

 expansion of the blood, from the heat acting on the contents of the 

 skull, the capacity of which is unchangeable. This coup de soleil oc- 

 curs still more frequently in the tropics, amongst troops on the march, 

 or amongst coolies or slaves working on railways or plantations. In 

 Pekin, during about ten days in July, 1743, the thermometer stood at 

 the extreme height of 104 in the shade, and in that period 11,400 

 people died. Under extreme elevations of temperature, the only safety 

 consists in retiring to the protection of houses, and in reducing the 

 temperature of the atmosphere in them by artificial methods, such as 

 by the use of large fans or punkahs, wet hangings, and other means. 

 Habit accustoms the Chinese, negroes, and others, to bear a greater 

 heat than the natives of temperate climates can support. 



Theories of Animal Heat. 



Previously to the time of Lavoisier, the heat of the body was more 

 or less vaguely referred to friction, the organic processes of nutrition, 

 the influence of nervous action, and generally to what was understood 

 as the action of the so-called vital force. 



In consolidating the discoveries of his predecessors, in regard to the 

 chemical nature of carbonic acid, oxygen, and nitrogen, and in explain- 

 ing therefrom the chemical processes and products of respiration, 

 Lavoisier propounded, for the first time, a distinct scientific theory of 

 the production of animal heat. This, now known as the cliemical theory 

 of animal heat, regards this heat as the result of an oxidation or com- 

 bustion process, affecting the animal frame. Carbon, when heated in 

 the presence of oxygen, unites with that gas, forms carbonic acid, and 

 evolves heat. In like manner, Lavoisier argued, that the formation of 

 carbonic acid in the blood, as the result of respiration in living animals, 

 must be accompanied by an evolution of heat. 



Though Lavoisier was wrong in supposing that this union of oxygen 

 with carbon takes place in the pulmonary capillaries, nevertheless, his 

 chemical theory of respiration is, with certain modifications and exten- 

 sions, accepted as the true theory of animal heat. 



To found this theory of respiration it was necessary to compare the 

 amount of heat evolved, during the direct combination of a certain 

 quantity of oxygen and carbon out of the body, with the amount of 

 heat given off from a living animal during its consumption of a similar 

 quantity of oxygen. This inquiry was surrounded by many difficulties. 



To obtain data for these purposes, Lavoisier made the first step in 

 the science of calorimetry, by burning given quantities of carbon and 

 hydrogen, in his so-called ice calorimeter. This was a closed metal 

 case with double sides, between which ice was packed; the source of 

 heat to be subjected to experiment was placed in the interior of the 

 case, and the quantity of heat given off was estimated by the quantity 

 of ice which was melted. The water calorimeter of Count Rumford 

 is constructed on a similar plan, but is filled with distilled water of a 

 known temperature, and measures the quantity of heat given out in 

 the experiment, by the elevation of temperature of a known quantity 

 of water. 



