PROPERTIES OF THE BLOOD, 



CHAPTER I. 



OF THE SEPARATION OF THE SERUM; THE COLOUR OF THE 

 CRASSAMENTUM; AND OF THE CAUSES OF THE COAGULATION 

 OF THE BLOOD. 



WHEN fresh blood is received into a basin, and suffered to 

 rest, in a few minutes it jellies or coagulates, and soon after 

 separates into two parts, distinguished by the names of crassa- 

 mentum and serum. These two parts differ in their propor- 

 tions in different constitutions : in a strong person the crassa- 

 mentum is in greater proportion to the serum than in a weak 

 one ; and the same difference is found to take place in dis- 

 eases ; thence is deduced the general conclusion, that the less 

 the quantity of serum is in proportion to the crassamentum, 

 bleeding, diluting liquors, and a low diet, are the more neces- 

 sary; whilst in some dropsies, and other diseases where the 

 serum is in a great, and the crassamentum in a small propor- 

 tion (i), bleeding and diluting would be highly improper. As 



(i.) It is not easy to ascertain exactly the proportion of serum, 

 because, as Dr. Davies a observed, the more the fibrin contracts the 

 more serum it presses out. By adding weak saline solutions or urine 

 to blood newly drawn, I found that the size of the crassamentum was in- 

 creased and the quantity of fluid separated decreased. 5 Dr. Davy c has 



a Essays on the Human Blood, p. 18, 8vo, b Edin. Med. & Surg. Journ. Ixiv, 369-71. 

 Lond. 1760. c Researches Phys. and Anat. ii, 28. 



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