THE PHYSIOLOGY OF THE BLOOD. 
391 
influence of circulation ; but it is not essentially, so, fluidity 
being only necessary for its motion, distribution, and the easy 
separation of its parts. Were it not so, how could it be pro- 
pelled through flexible tubes over every part of the body, or 
divided as the vessels branch off? How could it pass through 
the smaller vessels, or admit of the various separations of its 
parts, which are to produce the increase and repair of the whole 
body ? How could it be adapted for furnishing the various 
secretions, or be returned to the heart ? 
The fluid state of the blood undoubtedly depends on the vital 
principle, and its immediate connexion with the formation of 
living parts. It has been said, that its constant motion, and its 
being continually in contact with living parts, were the principal 
causes ; but that motion cannot have much to do with it, a few 
well known facts will tend to confirm. It remains fluid some 
days in persons in trances, where, to all appearance, it is per- 
fectly at rest, and no action of the vessels is going on : even in ex- 
travasation, or accumulation of it in large quantities in different 
cavities of the body from the rupture of some vessel, and where it 
could have no motion depending on the vessels, blood has continued 
fluid some weeks, and in that state has been absorbed. Indeed, 
the fact of its coagulating when abstracted from the body is a 
proof of its vitality, and that after the death of the animal it coa- 
gulates even when exposed to the same chemical influences as 
when living. 
The general and chemical Properties of the Blood. 
The blood, while circulating, appears to be a homogeneous 
liquid ; but when examined by the aid of a powerful microscope, 
it is found to be mechanically divisible into two parts ; the one 
essentially liquid, called liquor sanguinis; the other essentially 
solid, suspended in the former, and imparting its red colour. 
The liquor sanguinis consists of fibrine, held in solution with albu- 
minous, oleaginous, and saline matters by means of water. The 
solid partis composed of red globules made up of a central nucleus 
of fibrine, with an envelope or film of colouring matter, which 
last is not essential to the formation of blood, as in cold-blooded 
animals it is colourless. It is the opinion of some, that it im- 
parts strength, as animals of great strength and exercise have 
more than weak ones, and wild animals more than tame ones, and 
from the strongest muscles and those most in action being most 
supplied with it. But the same is found in white-blooded ani- 
mals, in which those parts most called into action are supplied 
with white blood ; especially some powerful fish. It is true they 
