THE BLOOD. 81 



of the mucilaginous part of the serum, or is a diluted serum, 

 with the addition of an expressed oil, or with a saccharine 

 substance instead of the neutral salts. 



But although there is an analogy between milk and diluted 

 serum, in the circumstance of coagulation, yet they differ in 

 another, namely, diluted serum can by a moderate heat be in- 

 spissated without coagulating, or forming any pellicle on its 

 surface ; but if milk be exposed to the same heat, it is not in- 

 spissated so completely ; for a pellicle is formed on its surface 

 in proportion as the evaporation takes place, and this pellicle 

 seems to be as perfectly coagulated as if the milk had been 

 exposed to a boiling heat ; for it will not dissolve again merely 

 by adding water, as inspissated serum does. 



Serum, therefore, by being diluted, comes near to milk in 

 the circumstance of its coagulation. But the coagulable lymph 

 cannot, by any art yet discovered, be made exactly to resemble 

 serum (LVI). 



The mixture with neutral salts makes it indeed so far ap- 



(LVI.) According to the views of M. Denis, a the liquid mixture of 

 coagulable lymph and a neutral salt is but serum with an excess of 

 fibrin, which he regards as identical with albumen, and ready to be 

 precipitated or coagulated under certain circumstances. See Notes 

 VTI, xu, xvi, and xvm. Scherer b regards fibrin of arterial blood 

 as distinct from fibrin of venous blood, because he finds the first in- 

 soluble and the next soluble in a saline solution. He attributes the 

 difference to the action of oxygen, stating that fibrin is deposited from 

 its saline solution after exposure to the air ; and that the fibrin of ve- 

 nous blood, after having been some time exposed to the air, is no longer 

 soluble in a solution of salt. I have kept slices of the buffy coat of 

 venous blood, without any obvious alteration, except a little swelling, for 

 months in saturated solutions of nitre, common salt, and Glauber's 

 salt ; the specific gravity of the solutions always became rather di- 

 minished. As mentioned in Note vin, fibrin certainly undergoes mo- 

 difications in its chemical properties some time after its coagulation. 

 Miilder, c in support of Scherer's view as to the action of oxygen on 

 fibrin, says that the protein compound which, during the coagulation 

 of the blood, is changed into fibrin, absorbs oxygen in the lungs, and 

 circulates through the arteries in the state of a bi-oxyde and of a trit- 

 oxyde of protein ; and that both of them, besides being ordinary con- 

 stituents of blood, exist in it to an increased extent during inflammation, 

 and form the chief part of the buffy coat. 



a Essaisur le Sang, pp. 81-4, 8vo, Paris, c Chem. of Vegetable and Animal Phys. 



1838. tr. by Dr. Fromberg, pp. 307, 314, 



b Dr. Turner's Elements of Chemistry, 316, 341, 8vo, part ii. 



8vo, Lond. 7th ed. 1842, p. US8. 



6 



