TRANSACTIONS OF SECTION A. 545 



also be proper to mention that an animal of tie same species placed in water at 61'' 

 was found to be nearly Gl:j° at the surface, and internally it was (i6i°. 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 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 114°, 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. 



o o 



In 5 minutes the dog was 108, water 112 



„ 6 „ „ 109, ,. 112 



i» 11 „ ,1 108, „ 112, the respiration having become very rapid. 



„ 13 ,, „ 108, ,, 112, the respiration being still more rapid. 



II 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 distinguish between 

 them. It is proper to observe that the animal which was the subject of this ex- 

 periment had been previously weakened by losing a considerable quantity of blood 

 a few days before. When the experiment was repeated witli dogs which had not 

 suifered 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 re- 

 peated six times, the alteration was so remarkable that the blood which was taken 

 in the warm bath could readily be distinguished from that which had been taken 

 from the same vein before immersion by those who were unacquainted with the 

 motives or circumstances of the experiment. 



' To discover whether a similar change would be produced in the colour of the 

 venous blood in hot air, a dog at 102° was placed in air at 134°. In ten minutes 

 the temperature of the dog was 104^°, that of the air being 130^ In fifteen minutes 

 the dog was 106°, the air 130°. A small quantity of blood was then taken from 

 the jugular vein, the colour of which was sensibly altered, being much lighter than 

 in the natural state. The effect produced by external heat on the colour of the 

 venous blood seems to confirm the following opinion which was first suggested by 

 my worthy and ingenious friend, Mr. Wilson, of Glasgow. Admitting that the 

 sensible heat of animals depends on the separation of absolute heat from the blood 

 by means of its union with the phlogistic principle in the minute vessels, may 

 there not be a certain temperature at which that fluid is no longer capable of 

 combining with phlogiston, and at which it must of course cease to give ofl' heat ? 

 It was partly with a view to investigate the truth of this opinion that Dr. Craw- 

 ford was led to make the experiments recited above.' 



These views of Dr. Crawford and 'his worthy and ingenious friend, Mr. Wilson ^ 

 of Glasgow,' express, about as well as it was possible to express before the chemical 

 discoveries of carbonic acid and oxygen, the now well-known truth that oxygen 

 carried along, but not chemically combined, with food in the arteries, com- 

 bines with the carried food in the capillaries or surrounding tissues in the outlyino- 



' Who, no doubt, was Dr. Alex. Wilson, first professor of astronomy in the 

 University of Glasgow (1760-1784); best known now for his ingenious views 

 regarding sunspots. 



1902. ^ N 



