548 PRACTICE OF PHYSIC. 



and cold may on different occasions arise from the same temper- 

 ature, as marked by the thermometer. 



With respect to this, however, it is to be observed, that 

 though every change of temperature gives a sensation of cold 

 or heat, as it is lower or higher than the temperature applied 

 immediately before, the sensation produced is in different cases 

 of different duration. If the temperature at any time applied 

 is under 62, every increase of temperature applied will give a 

 sensation of heat ; but if the increase of temperature does not 

 arise to 62, the sensation produced will not continue long, but 

 be soon changed to a sensation of cold. In like manner, any 

 temperature applied to the human body, lower than that of the 

 body itself, gives a sensation of cold ; but if the temperature ap- 

 plied does not go below 62, the sensation of cold will not con- 

 tinue long, but be soon changed to a sensation of heat. 



It will appear hereafter, that the effects of the sensation of 

 cold will be very different, according as it is more permanent 

 or transitory. 



XC... Having thus explained the operation of cold as absolute 

 or relative with respect to the human body, I proceed to men- 

 tion the general effects of cold upon it. 



1. Cold, in certain circumstances, has manifestly a sedative 

 power. It can extinguish the vital principle entirely, either in 

 particular parts, or in the whole body ; and considering how 

 much the vital principle of animals depends upon heat, it can- 

 not be doubted that the power of cold is always more or less 

 directly sedative. 



This effect may be said to take place from every degree of ab- 

 solute cold ; and, when the heat of the body has upon any oc- 

 casion been preternaturally increased, every lower temperature 

 may be useful in diminishing the activity of the system ; but it 

 cannot diminish the natural vigour of the vital principle, till the 

 cold applied is under 62 ; nor even then will it have this effect, 

 unless the cold be of an intense degree, or be applied for some 

 length of time to a large portion of the body. 



2. It is equally manifest, that, in certain circumstances, cold 

 proves a stimulus to the living body, and particularly to the 

 sanguiferous system. 



It is probable, that this effect takes place in every case in 



