34 



temperature, then the tendency to its diminution originating 

 from the chilling of one hand may exist without producing any 

 effect. We have there two causes acting in opposite directions, 

 and if they are equal they annihilate each other. If they are 

 unequal, we perceive only the difference between them. When 

 these two causes act in the same direction, then their efforts are 

 added to one another, and it is probably in a circumstance of 

 that kind that I have once found a diminution of 1 F. (0.56C,) 

 taking place in the mouth. 



We have now to examine how the diminution of the temperature 

 of a hand is produced when the other hand is dipped into cold 

 water. A priori it is evident that the chilling of the hand kept 

 in the air exists in consequence, either of the arrival of a cooler 

 blood, or in the diminution in the quantity of blood. That hand 

 being exposed to a cold air (for it is only in such a case that the 

 experiments succeed) loses its temperature by the action of that 

 cold air. At first the blood that arrives in the hand is not 

 cooler, as Edwards had supposed it was. This we prove by the 

 fact that the temperature is but very little changed in the mouth. 

 The supposition then remains that the quantity of blood ar- 

 riving in the hand is smaller than usual. This may happen by 

 two modes, one of which is that the heart sends less blood, and 

 the other that the blood-vessels of the hand are contracted and 

 prevent, in part, the passage of blood. It is certain that the 

 heart continues perceptibly to send the same quantity of blood. 

 Therefore we are induced to admit that the hand's blood-vessels 

 are contracted. But now what is the cause of that contraction ? 

 We will try to show that it is in an action of the nervous sys- 

 tem. Every one knows that under the influence of a sensation 

 or of emotion, the hands, and sometimes the feet, become cold. 

 The nervous system, in consequence of that sensation or emotion, 

 acts upon the blood-vessels and excites them to contract. The 

 calibre of the visible vessels is sensibly diminished. The same 

 phenomena take place in the two hands when one is dipped into 

 very cold water. An exceedingly violent pain is felt, the nervous 

 centres are strongly excited, and they act then as under the in- 

 fluence of an emotion. Dr. Tholozan and myself have observed 

 that the greater the pain felt, the more the temperature was di- 

 minished in the hand left in the air. 



