VOL. LX.XI.] PHILOSOPHICAL TRANSACTIONS. 151 



or producing cold, when immersed in warm water : and the experiments of Dr. 

 Fordyce prove, that the human body has the same power in a moist as well as in 

 a dry air : it is therefore highly probable, that this power does not depend solely 

 on evaporation. 



It may not be improper here to observe, that healthy frogs, in an atmosphere 

 above 70°, keep themselves at a lower temperature than the external air, but are 

 warmer internally than at the surface of their bodies : for when the air was 77°, 

 a frog was found to be 68°, the thermometer being placed in contact with the 

 skin ; but when the thermometer was introduced into the stomach, it rose to 

 70°4-. It mav also be proper to mention, that an animal of the same species 

 placed in water at 6l°, was found to be nearly 6l°J- at the surface, and internally 

 it was 66°-±-. These observations are meant to extend only to frogs living in air 

 or water at the common temperature of the atmosphere in summer. They do 

 not hold with respect to those animals, when plunged suddenly into a warm 

 medium, as in the preceding experiments. 



To determine whether other animals also have the power of producing cold, 



when surrounded with water above the standard of their natural heat, a dog at 



102° was immersed in water at 1 14°, the thermometer being closely applied to 



the skin under the axilla, and so much of his head being uncovered as to allow 



him a free respiration. 



In 5 minutes the dog was 108°, water 112° 



6 10.9 112 



11 1 OS 112 the respiration having become very rapid. 



13 108 112 the respiration being still more rapid. 



30 109 112 the animal then in a very languid state. 



Small quantities of blood being drawn from the femoral artery, and from a 

 contiguous vein, the temperature did not seem to be much increased above the 

 natural standard, and the sensible heat of the former appeared to be nearly the 

 same with that of the latter. 



In this experiment a remarkable change was produced in the appearance of 

 the venous blood : for it is well known, that in the natural state, the colour of 

 the venous blood is a dark red, that of the arterial being light and florid ; but 

 after the animal, in the experiment in question, had been immersed in warm 

 water for half an hour, the venous blood assumed very nearly the hue of the 

 arterial, and resembled it so much in appearance, that it was difficult to distin- 

 guish between them. It is proper to observe, that the animal which was the 

 subject of this experiment, had been previously weakened by losing a consider- 

 able quantity of blood a few days before. When the experiment was repeated 

 with dogs which had not suffered a similar evacuation, the change in the colour 

 of the venous blood was more gradual ; but in every instance in which the trial 

 was made, and it was repeated 6 times, the alteration was so remarkable, that 



