ANIMAL HEAT. 267 



The amount of warmth thus lost will vary with the degree of external 

 cold and other conditions influencing the abstraction of heat. 



Local Elevation of Temperature by Increased Circulation. If the 

 circulation be increased in any part of the integument, the effect pro- 

 duced is a local rise of temperature. This was shown by Bernard in 

 his experiments on division of the sympathetic nerve. In the rabbit 

 this operation produces a relaxation of the blood-vessels on the corre- 

 sponding 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, perceptible both by the touch and by the thermometer. 

 After section of the sympathetic nerve on the right side, the tempera- 

 ture of the corresponding ear was increased from 25 to 32 C. ; the 

 difference between the two sides being usually more marked in a cold 

 atmosphere. As the superficial parts of the body are habitually cooler 

 than the internal, from their exposure to the air, and as they are 

 constantly supplied with warm blood from the interior, their tempera- 

 ture will be raised by an increase in the amount of blood circulating 

 through them. The rise of temperature in these cases is a passive one, 

 the exposed tissues being warmed at the expense of the blood coming 

 from the interior. Xo more heat is produced than usual, and the cooling 

 effect of the air on the surface is unchanged ; but it is less perceptible 

 in the part subjected to experiment, owing to its increased supply of 

 blood, and the larger quantity of heat brought to it in a given time. 



The influence of the circulation upon the temperature of the external 

 parts has been shown by Mitchell * in observations on 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, suffi- 

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

 abolished the temperature of the corresponding hand rises 1.10 or 

 even 2.20 3 . But if the arm be emptied of blood, the tourniquet 

 applied, and the ulnar nerve then chilled to insensibility, the temper- 

 ature of the hand no longer rises, but falls, as before, 0.55. This 

 shows that the rise of temperature^ in the second experiment, was due 

 to increased circulation of blood in the paralyzed parts. 



In the glandular organs, on the other hand, when in functional activ- 

 ity, the rise of temperature is an active one, taking place in the sub- 

 stance of the gland itself; since the blood passing through these organs 

 becomes warmer instead of cooler, and receives heat from changes 

 taking place in the glandular tissue. 



Equalization of Bodily Temperature by the Circulation. As the 

 production of heat varies in different parts, according to their nutritive 

 changes, the blood acquires a higher temperature in some organs than 



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



