BLOOD. 259 



which exists in blood plasma and which can be removed by 

 beating the blood during clotting. Blood serum thus differs 

 from blood plasma in containing no fibrinogen and a smaller 

 quantity of calcium, magnesium, and phosphoric acid. 



Blood serum is of a sticky consistency, of alkaline reaction, 

 and has a specific gravity of about T028. It contains fats, 

 soaps, cholesterol, C 26 H 43 OH, lecithin, C 2 H 4 (OH)(CH 3 ) 3 N. 

 HP0 4 .C 3 H 5 :(C 18 H a5 2 ) 2 , albuminoids, glucose, traces of urea, 

 uric acid, creatin, lactic acid, and hippuric acid. 



The following analyses of serum were made by Hammar- 

 sten : 



Serum from 

 blood of- 

 Man 



Horse 



Ox 



Hen 



The ash of serum (about *85 %) consists chiefly of common 

 salt (-6 to ?%), 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 conditions 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- 

 albumen, sugar, gum, glycerine, or oil. Coagulation is facili- 

 tated by warmth, by contact with foreign bodies (e.g., by 

 stirring or beating), by free admission of air, by addition of a 

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

 alum, &c. 



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, produced 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 theorv has not received much support. 



s 2 



