4. DESCRIPTION OF THE BLOOD. 
capable of enlargement according to the amount of liquid which they are called upon 
to hold. In some animals, such as the cow, these reservoirs are extremely large, being 
capable of containing at least a quart of milk. The reservoirs are much smaller towards 
the mamina itself, and serve as tubes for the conveyance of the milk into the mouth 
of the young. Of the milk itself we shall speak in another part of the work. 
The BLoop of the Vertebrate animals is of a light red colour when freshly drawn 
from the arteries. This wondrous fluid, in which is hidden the life principle that 
animates the being, is of a most complex structure, as may be imagined when it is 
remembered that all the parts of the body are formed from the blood; and there- 
fore to give a full description of that fluid would occupy more space than can be 
afforded to one subject. It is, however, so important a substance that it demands some 
notice. 
When it is freshly drawn, the blood appears to be of an uniform consistence, but if 
poured into a vessel and suffered to remain undisturbed it soon begins to change its 
aspect. A comparatively solid and curd-like mass, of a deep red colour, rises to the 
surface, and there forms a kind of cake, while the liquid on which it floats 1s limpid and 
almost colourless. The solid mass is called the clot, and the liquid is known by the 
name of serum. The whole time consumed in this curious process is about twenty 
minutes. While thus coagulating the blood gives out a peculiar odour, which, although 
far from powerful, can be perceived at some distance, and to many persons is 
inexpressibly revolting. 
The upper part of the clot is covered with a thick film of an elastic and tenacious 
nature, which can be washed free from the red colouring substance, and then appears of 
a yellowish white tint. It can be drawn out and spread between the fingers, as if it 
were an organic membrane ; and, as its particles arrange themselves into fibres, the 
substance is called fibrin. When a portion of fibrin is drawn out until it is much 
lengthened, the fibres are seen crossing each other in all directions, sometimes forming 
themselves into regular lines. 
The red mass, which remains after the fibrin and serum have been removed, is almost 
wholly composed of myriads of small rounded bodies, called corpuscules, which can be 
readily seen by spreading a drop of blood very thinly on glass, and examining it with a 
microscope. The general appearance of the blood corpuscules 
of man is seen in the accompanying illustration. Some of the 
disc-lke corpuscules are seen scattered about, while others 
have run together and adhered by their flat sides, until they 
look somewhat like rouleaux of coin. There is sufficient dis- 
tinction between the blood corpuscules of the-various Mammalia 
to indicate to a practised eye the kind of animal from which 
they were taken; while the blood of the four great divisions of 
the Vertebrates is so strongly marked, that a casual glance will 
detect the ownership of the object under the microscope. The 
BLOOD CORrUSCULES OF MAN. specimen represented above is magnified about two hundred 
diameters. The blood corpuscules of the Mammalia are cir- 
cular, while those of the other three divisions are more or less elliptical. 
That the blood contains within itself the various substances of which the body is 
composed, is evident to the intellect, although as yet no investigator has discovered the 
mode of its operation. 
How the blood corpuscules are generated from the vegetable and animal substances 
taken into the stomach, we know not; but we do know that each globule possesses life, 
passing through its regular stages of birth, development, age, and death. When yet in 
their first stages of existence, the blood corpuscules are colourless, not taking the well-known 
ruddy tint until they have attained their full development. The living current that passes 
through our bodies is truly a fathomless ocean of wonders! Even the material formation 
of this fluid is beyond our present sight, which cannot penetrate through the veil which 
conceals its mysteries. Much less can we explain the connexion of the blood with the 
mind, or know how it is that one thought will send the blood coursing through the frame 
