PHYSIOLOGY OP THE BLOOD. 
392 
have red blood, but that supplies the viscera and those parts which 
have the least powerful action to perform. In the cases above- 
mentioned the particular redness is caused by their great supply 
of blood, so that the argument, in my opinion, is controverted. 
Sir E. Home supposes the red part which envelopes the glo- 
bule may be for the purpose of keeping them separate, and thus 
assist in preventing coagulation while circulating. He also re- 
marked, that while the globules are enveloped in their colouring 
matter they are not seen to run together on the field of the 
microscope ; but when deprived of it they seem to attract and be 
attracted so as to unite themselves together, and form a mass. 
According to some physiologists these globules have different 
shapes ; but the generally received opinion is, that in birds and 
cold-blooded animals they are elliptical and flattened ; and in the 
mammiferous, spherical and flattened. By the calculation of Dr. 
Wollaston, the globule of human blood is about T ^Vo part of an 
inch in size. 
On the abstraction of blood from an animal a mechanical sepa- 
ration of its parts takes place, dividing it into serum and crassamen- 
tum, which last is divided into fibrine and colouring matter. This 
process is termed coagulation. To account entirely for the pro- 
perty of coagulation would be difficult and perhaps impossible ; 
but many have attempted it, and I will give you the result as far 
as it agrees with my views. It is not confined to the blood when 
out of the body. The importance of this property is evident ; for 
if it did not coagulate, the existence of animals would be most 
precarious, since on the slightest injury they would be liable to 
bleed to death ; therefore in cases of haemorrhage it is essential. 
It appears that fluidity was only intended for its motion, and its 
motion is to carry life and living materials to every part of the 
body : these materials, when carried, become solid, so that 
solidity is the ultimate end of the blood. 
Its coagulation out of the body undoubtedly is occasioned, 
for the most part, by the vital principle not being communicated 
as in the body ; for when extravasated in the living subject, it 
does not coagulate so rapidly ; indeed, it remains fluid some 
considerable time : also when an artery is secured by two ligatures, 
the blood retained between them continues fluid a long time. 
When abstracted from the body it may be influenced by various 
circumstances. The application of heat hastens coagulation : 
when contained in the exhausted receiver of an air pump it coagu- 
lates more quickly than when exposed to the atmosphere. When 
received into a narrow spherical vessel, its coagulation appears to 
be quickened, as the particles of fibrine are not so far removed 
from a common centre, therefore are more powerfully attracted 
