CHEMICAL COMPOSITION OF BLOOD 



49 



which can be precipitated from its saline solution by dialyzing off the 

 salts, and pseudo-globulin, which cannot be so precipitated. 



In addition to the nitrogen represented as protein, serum (or plasma) 

 contains non-protein nitrogen, the amount of which varies with the 

 nature of the food and the stage of digestion. Part of this fraction is 

 attributable to urea and other metabolites on their way to be excreted, 

 but another portion, and an important one, is due to amino-acids 

 absorbed from the intestine during the digestion of proteins and on 

 their way to be utilized in the tissues. 



Of the inorganic salts of serum, the most important are sodium 

 chloride and sodium bicarbonate. Small amounts of potassium, 

 calcium, and magnesium, united with phosphoric acid or chlorine, and 

 a trace of fluoride, are also present. A portion of the salts is loosely 

 combined with the proteins. 



Our knowledge of the chemistry of the circulating plasma is likely 

 to be notably augmented by the method of vivi-diffusion recently intro- 

 duced by Abel. An artery of an anaesthetized animal is connected by 

 a cannula to a system of celloidin tubes immersed in a saline solution. 

 Blood passes from the artery through the tubes, where it exchanges 

 diffusible constituents with the solution, and is then returned to the 

 animal's body by another cannula attached to a vein. Coagulation 

 of the blood in the apparatus is prevented by hirudin, and under 

 aseptic conditions the circulation may proceed through the tubes for a 

 long time. The saline solution can then be analyzed for substances which 

 have entered it from the blood amino-acids, for example (Fig. n). 



The following tables give some details of the composition of blood : 



i.ooo GRAMMES OF PIG'S BLOOD (CORPUSCLES, 435*09; SERUM, 



CONTAINED - 



PROTEINS OF PLASMA IN 1,000 GRAMMES. 



* The pig's erythrocytes are peculiar in that the sodium appears to be 

 entirely confined to the plasma. 



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