24 
CONSTITUENTS OF BLOOD. 
decomposition of protein by the alkalies. Neither chondrin nor gelatin yield protein when 
treated with potash, as they do not become purple with hydrochloric acid. Gelatin does 
not contain fibrin, albumen or casein. Blood, therefore, can not be formed from gelatin; 
and hence an animal, fed exclusively upon it, must die from starvation. Though proteine 
compounds can not be evolved from gelatin, yet gelatin is formed from the proteine bodies. 
We have an example of such a production in the chick in the egg. 
BLOOD. 
It is a compound substance, though homogeneous when flowing either in its appropriate 
vessel, or in the moments during which it is issuing from a wounded vessel. When it has 
stood a short period, however, it separates spontaneously into three parts : serum, which 
is a yellowish somewhat viscid fluid ; fibrin, a fibrous white coagulated mass; and blood 
globules of a red color, which, when circulating, impart a scarlet red to the whole mass. 
Blood, however, is not necessarily red : the white fluid of mollusca, and other invertebrate 
animals, is a true blood. It is also of different colors in insects and worms, as green, 
yellow, orange. 
The temperature of blood varies in different classes of animals : in the ox, it is 103° ; 
in the hog, 99*5° ; horses, 96• 8° ; sheep, 101'3° ; and the duck, 105’8°, being uniformly 
higher in birds than in mammalia. Arterial blood is 1’8° higher than venous. Its specific 
gravity varies from 1‘041 to 1’082. In robust men, it is high; in very young infants, 
thin, and of a low specific gravity. 
The function of the blood is to transmit nutritive matter to the various parts of the sys¬ 
tem. It must be nutritive itself; and as there is a continual waste in the system, it must 
necessarily receive continual additions : these are furnished by digestion, or, in vegetables, 
from matter taken up by the roots. The nutritive matter of blood consists of plasma , as it 
is sometimes called, and which is itself composed of albumen, fibrin, casein, fat, salts, 
iron, extractive matter, and a peculiar coaling substance called hcemaphcein *. These 
constituents, however, are not all nutritive. As certain bodies are carried out of the system 
in a healthy state, we are to regard them as in a condition unsuited for nourishment : thus 
saline, coloring and extractive matter are excreted; while albumen, fibrin, and fat, never 
are, except in a morbid state. They neither are found in sweat, urine or mucus. 
The nutritive power of the blood depends upon the food, and the health or normal 
functions of the system. We may form some opinion upon this subject, from the composi¬ 
tion of blood from a horse. 
Simon’s Chemistry, Vol. I, p. 101, 102. 
