THE BLOOD, ITS NATURE AND COMPOSITION. 55. 



heat; and although it is the source whence other fluids are 

 obtained, it is yet a fluid sui generis, differing from all others. 



Soon after it is drawn from the body it coagulates, and then 

 separates into two parts, — the Serum, a watery colourless fluid 

 which floats on the top, and the Crassamentum, which appears 

 of a firm consistency and a red colour. The serum is a peculiar 

 fluid, and may be separated into its constituent principles. If 

 subjected to a temperature of 150° a portion is converted into 

 a substance resembling albumen, or the white of an egg ; the 

 other poi'tion remains fluid, and is termed the serosity of the 

 blood, and is that which constitutes the gravy in meat. The 

 serum contains several salts in solution, the most abundant of 

 which is soda. 



The Crassamentum is likewise divisible into two portions ; the 

 Cruor, which gives to the blood its purple hue ; and the Lymph, 

 which is more solid in its nature, and is considered the basis of 

 the coagulum. The latter can be separated from the former by 

 washing, and it likewise separates when the blood is a long time 

 coagulating, in which case the red portion of the blood, being 

 the heaviest, falls to the bottom of the vessel, leaving the lymph 

 on the top. The cruor, or red portion of the blood, has been 

 found, on submitting it to a microscope, to be composed of 

 globules, which are su])posed to be each about the thi'ce or four 

 thousandth part of an inch in diameter. It is therefore to these 

 globules that the blood owes its redness ; but the intensity of the 

 colour is subject to great variation, being darker in animals that 

 are poorly fed ; or when exposed to carbonic acid ; and becoming 

 more florid in others that are well fed ; and also when exposed 

 to oxygen, or to atmospheric air. 



The other part of the crassamentum, the lymph, Avhich, from 

 its nature, is also called Fibrin, is, in fact, the most important 

 of all ; for it is that which mainly supplies the different parts of 

 the body, particularly the muscles, with nutriment, and repairs 

 wounds and fractures in an extraordinary manner. Unlike the 

 cruor, it exists in the blood of all animals, and in every part of 

 the system. Some animals have entirely white blood, the cruor 

 being absent ; and in red-blooded animals there are some por- 

 tions of the body, such as the white of the eye, where the 

 vessels are so small that they do not admit the red globules. 



The specific gravity of the blood rather exceeds that of water ; 

 but venous blood is somewhat heavier than arteriak 



The temperature of the blood varies in difterent animals; in 

 man it is 90°, but in the horse upwards of 100°. It is rather 

 warmer in the arteries than in the veins, and is liable to variation 

 from disease, it having been found in severe inflammations to be 

 raised 7° in man, and in the cold fit of agues 4° lower than in a 

 state of health : it is, however, but slightly raised or depressed 



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