Animals pojfefs of producing Cold. 
detached from the air, the arterial blood when it returns by the 
pulmonary vein will have its fenfible heat greatly diminifhed, 
and will confequently abforb heat from the veffels which are in 
contad with it, and from the parts adjacent. The heat which 
is thus abforbed in the greater veffels will again be extricated 
in the capillaries, where the blood receives a frefh addition of 
phlogifton. If, in thefe circumftances, the blood during each 
revolution were to be equally impregnated with this latter prin- 
ciple, it is manifeff, that the whole effed of the above procefs 
would be to cool the fyftem at the center, and to heat it at the 
furface ; or to convey the heat to that part of the body where 
it is capable of being inftantly carried off by evaporation. But 
it appears, from the experiments which have been laft recited, 
that, when an animal is placed in a heated medium, the fan- 
guineous mafs, during each revolution, \§ lefs impregnated with 
phlogifton ; for we have feen, that the venous blood, in thefe 
circumftances, becomes gradually paler and paler in its colour 
tillatTength it acquires very nearly the appearance of the ar- 
terial : and it is rendered highly probable by the experiments of 
Dr. Priestley, that the dark and livid colour of the blood in 
the veins depends upon its combination with phlogifton in the 
minute veflels. Since, therefore, in a heated medium, this fluid 
does not affume the fame livid hue, we may conclude, that it 
does not attract an equal quantity of the phlogiftic principle %: 
* It is of no confequence in the above argument, whether we fuppofe, with 
Pr. PRLfesTLEY, that the alteration of colour in the blood depends upon its com- 
bination with phlogifton in the capillary arteries, or maintain with foijne other 
philofophers that this alteration arifes from a change produced in the bibod itfelf by 
f|e a&ion of the veffels ; it is fufficicnt. for our purpofe to affume if as a facY, 
which, I thinlc, has been proved by direct’ experiment, ; that-, ''in the natural Ritte 
of- the- anitnalj 'the^blood undergoes' ^ change m-t-he bapparies],:’'hyj which. cjapgt 
city^ for containing heat diminifhed ; and that in a heated ryngji^rDy 4 [does not 
a fimilar change* 
S f 
i z 
It 
