Animals pojfefs of producing Cold. 487 
Small quantities of blood being drawn from the femoral 
artery, and from a contiguous vein, the temperature did not 
feem to be much increafed above the natural ftandard, and the 
fenfible heat of the former appeared to be nearly the fame 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 hate, 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 queftion, had been immerfed in warm water 
for half an hour, the venous blood affirmed very nearly the hue 
of the arterial, and refembled it fo much in appearance, that it 
was difficult to diftinguiffi between them. It is proper to ob~ 
ferve, that the animal which was the fubjed of this experi- 
ment, had been previoufly weakened by loflng a conflderable 
quantity of blood a few days before. When the experiment 
was repeated with dogs which had not buffered a fimilar evacua- 
tion, the change in the colour of the venous blood was more 
gradual ; but in every inftance in which the trial was made, 
and it was repeated fix times, the alteration was fo remarkable, 
that the blood which was taken in the warm bath could readily 
be diftinguifhed from that which had been taken from the fame 
vein before immerflon, by thofe who were unacquainted with 
the motives or circumftances of the experiment. 
To difeover whether a fimilar change would be produced 
in the colour of the venous blood in hot air, a dog at 102° was 
placed in air at 13 4 0 . 
In ten minutes the temperature of the dog was 104T, that 
of the air being 130. In fifteen minutes the dog was io6°, the 
air 130°. A final! quantity of blood was then taken from the 
VoL» LXXL ~ Sff jugular 
