MODE OF PRODUCTION OF ANIMAL HEAT. 307 



It is evident, accordingly, that the evolution of heat in the living 

 animal is due to other causes than those which result in the immediate 

 production of carbonic acid. Even outside the body a notable elevation 

 of temperature may be produced by the hydration of quicklime, the 

 mixture of alcohol and water, or of sulphuric acid and water, as well 

 as other chemical or physical actions in which direct oxidation does not 

 take part. Many analogous changes may take place in the process of 

 internal nutrition, from which a part, at least, of the animal heat origin- 

 ates in the living body. 



Local Production of Heat in the Organs and Tissues Although 

 the living body, as a whole, presents a certain standard temperature, 

 the production of heat takes place separately in each organ and tissue 

 by the changes of nutrition which go on in its substance. This is 

 shown by the fact that each separate organ has a special temperature 

 of its own, which increases or diminishes according to its condition of 

 activity or repose. A very considerable quantity of heat is thus pro- 

 duced in the substance of the muscles. The experiments of Becquerel 

 and Breschet on the brachialis, in man, showed the temperature of this 

 muscle in repose to be 36.5 ; while, after repeated and energetic flexion, 

 it was from 37 to 37.5. Bernard, 1 by placing thermo-electric needles 

 in the two gastrocnemii muscles of the dog, after section of the spinal 

 cord to prevent voluntary movements, found the temperature of the 

 muscles on the two sides to be sensibly equal ; but on producing con- 

 traction by galvanizing one of the sciatic nerves, the temperature of 

 the muscle on that side rose from 0.1 to 0.2, at the same time that 

 the venous blood of the muscle became darker in hue. Since the 

 muscles constitute so large a part of the mass of the body, it is easy to 

 understand how continuous muscular exertion should, after a time, 

 produce a general elevation of temperature. In the muscles, during 

 contraction, the increase in warmth is always accompanied by a greater 

 consumption of oxygen, and consequently by a darker color of the 

 venous blood. 



Heat is also produced in the glandular organs when in active secre- 

 tion, as shown by comparing the temperature of the arterial blood enter- 

 ing with that of the venous blood leaving the glandular tissue. Under 

 these circumstances the venous blood coming from the gland is warmer 

 than the arterial blood with which it is supplied. According to the 

 observations of Bernard upon the submaxillary gland of the dog, while 

 the gland is in repose, the circulation through its tissue is slow, its 

 venous blood scanty and very dark-colored, and the oxygen of the arte- 

 rial blood is reduced, in traversing the organ, to 40 per cent, of its 

 original quantity ; but when the gland is excited to active secretion, its 

 circulation is increased in rapidity, its venous blood is more abundant 

 and of a brighter color, its oxygen being only reduced to 61 per cent, 

 of that contained in the arteries. At the same time its temperature 



1 Revue Scientifique. Paris, 1871, No. I., p. 1064. 



