20 THE BLOOD. 



Carbonic acid in solution. 



Urea, 0*177 parts per 1,000, in arterial blood; 0'088, in the blood of the renal vein. 



Urate of soda, proportion not determined. 



" potassa (probable), proportion not determined. 



" " lime, " " " " 



" " magnesia, " " " " 



" " ammonia, " " " " 



Sudorates of soda, etc., " " " 



Inosates, " " " 



u 



Oxalates, 

 H Creatinine, " 



Leucine, " " " 



Hypoxanthine, " " " 



Cholesterine, 0'455 to 0'751 parts per 1,000, in the entire blood. 



,, . ,, , ( Fibrin, 3 parts per 1,000. 



Plasmme, 25 parts (dried) per 1,000. J . 



| Metalbumen, 22 parts per 1,000. 



Serine, 53 parts (dried) per 1,000. 



(Moist fibrin, 8'820 parts per 1,000, in the entire blood. 



Metalbumen and serine constitute the albumen of the older analyses. Albumen, 



about 75 parts [dried] and 330 parts [moist] per 1,000, in the entire blood.) 



Peptones, 4 parts (dried) and 28 parts (moist) per 1,000. 



Coloring matters of the plasma, proportion and characters not determined. 



We shall take the above table as a guide for our study of the individual constituents 

 of the blood-plasma. As regards gases, in addition to carbonic acid, which we have 

 classed with the excrementitious matters, the blood contains oxygen, nitrogen, and 

 hydrogen. The nitrogen and hydrogen are not important, and the relations of oxygen 

 will be fully considered under the head of respiration. Most of the coloring matter of 

 the blood exists in the red corpuscles, which contain a peculiar principle which we 

 have already considered in connection with the chemical constitution of these bodies. 



In studying the composition of the blood, as well as the composition of food, the 

 tissues, secreted fluids, etc., it is convenient to divide its constituents into classes, and this 

 we have done in the simplest manner possible. 



It is evident, the blood receiving all the products of disassimilation as well as the 

 nutritive principles resulting from digestion, that there should be a division of its con- 

 stituents into nutritive and excrementitious. We have classed certain principles together 

 as excrementitious. These are the various products of disassimilation of the organism, 

 which are taken up by the blood or conveyed to the blood-vessels by the lymphatics, 

 exist in the blood in small quantity, and are constantly being separated from the blood 

 by the different excreting organs. Their constant removal from the blood is the expla- 

 nation of the excessively minute proportion in which they exist in this fluid. Their 

 relations to the organism will be fully considered under the head of excretion. 



Excluding, then, for the present, all consideration of the products of disassimilation, 

 we have to study the various constituents of the blood that are more or less directly 

 concerned in nutrition. 



Physiological chemists recognize certain constituents of the organism, called proxi- 

 mate principles, which may be elementary substances, but which are more frequently 

 compounds. We speak of chloride of sodium as a proximate principle existing in the 

 blood, because, as chloride of sodium, it gives to the blood certain properties. We do not 

 regard the chemical elements, chlorine and sodium, as proximate principles, because they 

 do not exist in the blood uncombined. Still, a proximate principle may be a chemical 

 element, as in the case of oxygen, which, as oxygen, performs, in the blood, certain 

 important functions. 



Adopting, in the main, the definition given by Eobin, we may regard as a proximate 



