266 



BLOOD 



The ash of serum (about 0*85 per cent) consists chiefly of common 

 salt (0*6 to 0'7 per cent), with small quantities of potash, lime and 

 magnesia. 



The rapidity with which blood coagulates after leaving the body 

 varies, as already stated, with different animals and with the condi- 

 tions under which it is kept. Coagulation is retarded by cooling, by 

 diminishing the amount of oxygen or increasing that of carbon dioxide, 

 by the addition of acids, alkalies, egg-albumin, sugar, gum, glycerine, 

 or oil. Coagulation is facilitated by warmth, by contact with foreign 

 bodies (e.g., by stirring or beating), by free admission of air, by addi- 

 tion of a small quantity of water, or by the addition of ferric salts, 

 alum, etc. 



The spontaneous clotting of blood after removal from the animal 

 is assigned to different causes by different authorities. According to 

 Schmidt it is due to the action of an enzyme fibrin- ferment, pro- 

 duced probably by the destruction of the white corpuscles, upon the 

 fibrinogen. Another view attributes to the separation of calcium 

 phosphate a large share in the process (Freund), while a third assigns. 

 oxidation as the chief cause. The last theory has not received much 

 support. 



The solid portion of coagulated blood consists chiefly of red and 

 white corpuscles entangled in a network of fibrin. 



The red corpuscles consist usually of circular, biconcave discs. In 

 birds, amphibia, fishes and some few mammals, e.g., the camel, they 

 are elliptical and biconvex. Their size varies considerably in different 

 animals, being largest in the amphibia. In man they have an aver- 

 age diameter of -007 to '008 millimetre ( = about -.r-i^ inch) and a 

 maximum thickness of '0019 millimetre. They are heavier than the, 

 plasma, having a specific gravity of about 1O9. 



The average number in the blood of man is about 5,000,000, in 

 that of woman about 4,000,000, per cubiq millimetre. By treatment 

 with water, ether, or other substances, blood corpuscles lose their 

 colouring matter and leave a residue known as the stroma of the red 

 corpuscles. This consists of nitrogenous matter and often retains the 

 form of the original corpuscles. 



The colour of blood depends upon hemoglobin and its compound 

 with oxygen oxy hemoglobin. Haemoglobin consists largely of albu- 

 min (about 96 per cent), the other characteristic component being a, 

 colouring matter known as h&mochromogen (about 4 per cent), con- 

 taining iron. 



Haemoglobin from different animals differs somewhat in composi- 

 tion. Hammarsten gives the following analyses : 



