THE BLOOD. 175 



CHAPTER IV. 



OF THE BLOOD. 



THE Blood, in the human subject, and in many animals, is of 

 a red colour. It is about the consistence of thin size, has a pe- 

 culiar smell, a nauseous and slightly saiine taste, and is some- 

 what heavier than water; its. specific gravity being about 105, 

 and its temperature in the living body is from 96 to 98 of Fah- 

 renheit. Its quantity is variously estimated at from eight to one 

 hundred pounds, so that there would seem to be no very exact 

 means of ascertaining this point. 



So long as it continues to circulate, or while it is still flowing 

 from an opened vessel, it has, to common inspection, the ap- 

 pearance of a homogeneous fluid; yet, after it has been drawn a 

 few minutes, and permitted to remain at rest, it assumes a thick 

 gelatinous condition, expressed by the term coagulation, and by 

 which it ceases to be any longer fluid. "The coagulation begins 

 on the surface of the mass, and by a thin pellicle, which shows 

 itself in three or four minutes; commonly at the end of twenty 

 minutes the coagulation is complete throughout, but this rule 

 varies according to the state of the body at the moment ; and 

 the coagulation is more protracted when the quantity of blood 

 is large and has been drawn through a large orifice, than where 

 it is small, arid has been evacuated through a small orifice. This 

 change has scarcely taken place, when a spontaneous separa- 

 tion follows, whereby it is resolved into a watery part called Se- 

 rum, and into a thick condensed -piass called Cruor or Crassa- 

 mentum. The serum first shows itself on the surface of the co- 

 agulum, in small drops, which quickly increasing in number and 

 size, finally run together, and form a mass of fluid exceeding 

 considerably that of the crassamentum. The separation into 

 serum and crassamentum, though sufficiently evident after a 

 few hours, yet requires some days for its complete accomplish- 

 ment; for the coagulum still continuing to contract, expels more 

 and more of the serum. 



The peculiar complexion of the blood depends upon a red co- 

 louring matter consisting in globules. This matter does not seem 



