24 CONSTITUENTS OF BLOOD. 



decomposition of protein by ihe 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 coloring 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. 



