14:6 THE BLOOD. 



Characters of the Serum. After coagulation, if the serum 

 be carefully removed, it is found to be a fluid of a color 

 varying from a light amber to quite a deep, but clear, red. 

 This depends upon a peculiar coloring matter, distinct from 

 hematine, but which has never been isolated. The specific 

 gravity of the serum is somewhat less than that of the entire 

 mass of blood; being, according to Becquerel and Rodier, 

 about 1,02s. 1 It contains all the principles found in the 

 plasma, or. liquor sanguinis, with the exception of the fibrin. 

 It can hardly be called a physiological fluid, as it is formed 

 only after coagulation of the blood, and never exists isolated 

 in the body. The effusions which are commonly called 

 serum, though they resemble this fluid in some particulars, 

 are not identical with it, being formed by a process of transu- 

 dation rather than separation of the blood, as in coagulation. 

 "We have already seen that, in the body, fibrin and albumen 

 are in combination, and that the organic principle of the 

 serum (albumen) when injected into the vessels of a living 

 animal does not become assimilated, but is rejected by the 

 kidneys. The serum must not, therefore, be confounded with 

 the plasma or liquor sanguinis, which is the natural clear 

 portion of the blood. 



Coagulating Principle in the Blood. Acquainted, as 

 we are, with the properties of fibrin, it is evident that this 

 principle is the agent which produces coagulation of the blood. 

 In fact, whatever coagulates spontaneously is called fibrin, 

 and whatever requires some agent to produce this change of 

 consistence is called by another name. But before the prop- 

 erties of fibrin were fully understood, the question of the 

 coagulating principle was a matter of much discussion. 2 

 Malpighi was probably the first to isolate this principle; 



1 Op. cit., p. 86. 



a An admirable historical review of the theories and discoveries relating to 

 the properties of fibrin and the coagulation of the blood is to be found in Mr. 

 Gulliver's introduction to the Sydenham edition of the works of William Hewson 

 London, 1846, p. 25 et seq. 



