310 ANIMAL HEAT. 



lungs, being rather more than counterbalanced by that lost from the 

 surface, the total effect upon the circulating fluid is a lowering of its 

 temperature. The amount of warmth thus lost will vary with the degree 

 of external cold and other conditions of the atmosphere which influence 

 the rapidity of the abstraction of heat. 



Local Elevation of Temperature by increased Circulation. If the 

 circulation be increased in any part of the external integument, the 

 immediate effect produced is a local rise of temperature. This was first 

 shown by Bernard in his experiments upon division of the sympathetic 

 nerve on one side of the neck. If this operation be performed upon the 

 rabbit, the consequence is a relaxation of the bloodvessels in the cor- 

 responding side of the head, an increased vascularity of the parts, most 

 readily seen in the semi-transparent tissues of the ear, and a higher 

 temperature, readily perceptible both by the touch and the thermometer. 

 In a rabbit, after section of the sympathetic nerve upon the right side 

 of the neck, the temperature of the corresponding ear, as indicated by 

 the thermometer, was increased from 25 to 32; and the difference 

 between the two sides is usually more marked as the external air is 

 colder. Since the superficial parts of the body are habitually cooler 

 than the internal on account of their exposure to the air, and as they 

 are constantly supplied with warm blood from the interior, their actual 

 temperature will be increased in proportion to the amount of blood cir- 

 culating through their vessels. The local rise of temperature in these 

 instances is a passive one, the exposed tissues being warmed at the 

 expense of the blood coming from the internal organs. No more heat 

 is actually produced in the body than usual, and the cooling effect of the 

 air upon the whole system is unchanged ; but it is less perceptible in 

 the part subjected to experiment, because it receives a larger quantity 

 of heat from the interior owing to the increased volume of blood passing 

 through it in a given time. 



This influence of the circulation upon the temperature of the external 

 parts has been shown by Dr. Wier Mitchell 1 by observations upon the 

 human subject. If the hand and arm be held for some moments above 

 the head, emptied as fully as possible of blood, and a tourniquet then 

 applied to the arm in such a way as to check the circulation, the tem- 

 perature of the hand falls 0.55. If, on the contrary, the circulation be 

 left unimpeded, and a freezing mixture applied to the elbow, sufficient 

 to chill the ulnar nerve, when sensation has become entirely abolished 

 the temperature of the corresponding hand rises from 1.10 to 2.20. 

 But if the arm be first emptied of blood as before, the tourniquet applied, 

 and the ulnar nerve then chilled to insensibility, the temperature of the 

 hand no longer rises, but falls, as in the former experiment, 0.55. 



In the internal or glandular organs, on the other hand, when ex- 

 cited to functional activity, the rise of temperature is an active one, 

 taking place in the substance of the gland itself; since the blood 



1 Archives of Scientific and Practical Medicine. New York, 1873, vol. i. p. 354. 



