132 PHYSIOLOGY CHAP. 



These figures show that sodium chloride is by far the most 

 abundant constituent of the ash of serum. It is held in simple 

 solution in the plasma or in the form of highly unstable compounds, 

 for when serum is dialysed in distilled water, osmotic equilibrium 

 between the two fluids is soon arrived at in regard to the chlorine. 



The greater part of the sodium of the ash exists in the form of 

 bicarbonate (Gtirber) in the plasma, a lesser amount being com- 

 bined with phosphoric acid in the form of di-sodic phosphate. 



It should be noted that potassium salts predominate in the 

 corpuscles, sodium salts in the plasma. 



The osmotic pressure of plasma depends largely upon the sum 

 of the inorganic matters which it contains ; it is, as we shall see, 

 of great importance in the metabolic exchanges between corpuscles 

 and plasma, and between plasma and tissues. 



The blood gases, as a whole, represent a very small part of the 

 weight of the blood (0'10-O15 per cent). They are oxygen, carbonic 

 acid, nitrogen, and also argon. The two first occur principally in 

 combination, the two last in simple solutions. Nitrogen and argon 

 are not known to fulfil any function in the animal economy; on 

 the other hand (as we shall find in discussing the Chemistry of 

 Respiration), oxygen and carbonic acid are of capital importance. 

 Here we must confine ourselves to stating that the combinations 

 which they form of oxygen with haemoglobin, and of carbonic acid 

 with haemoglobin and the alkalies, are very unstable, so that it is 

 possible with the vacuum to separate and estimate volumetrically 

 the whole of the gases contained in the blood. 



VI. After ascertaining the several constituents of the blood 

 corpuscles and blood plasma, it is easier to marshal the data 

 referring to the solution of the problem of Blood Coagulation, a 

 problem which is indeed one of the most difficult in physiological 

 chemistry. 



Although this problem has of late years been treated with 

 extraordinary acumen by a number of observers (e.g. A. Schmidt 

 in particular), we cannot at present claim to have established 

 any theory that is universally acceptable in all its details. 



In studying the phenomena of coagulation it is well to treat 

 the different questions and problems involved as if each were 

 separate and distinct in itself. 



(.) The first problem that presents itself is why, i.e. under 

 what conditions, the blood, which remains fluid so long as it 

 circulates within the vessels, coagulates spontaneously soon after it 

 leaves them. This question was attacked by Hewson in the 

 eighteenth century, while Briicke solved it more completely in 



1857. 



Clotting does not depend upon the cooling of the blood, for 

 when frozen before coagulation, it is found on thawing still to be 

 fluid, and clots soon after in the usual manner. Cooling, therefore. 



