COMPOSITION OF THE BLOOD-PLASMA. 21 



more or less intimately combined with the coagulable organic matters. Of 

 these, the sodium chloride is the most abundant. It undoubtedly has an im- 

 portant use in giving density to the plasma and in regulating the processes of 

 endosmosis and exosmosis. In connection with the organic salts and crystal- 

 lizable excrementitious matters, it may be stated, in general terms, that the 

 blood contains 14 to 16 parts per 1,000 of matters in actual solution, of which 

 6 to 8 parts consist of inorganic salts. The presence of these substances in 

 solution, with the organic coagulable matters, prevents the solution of the 

 corpuscular elements of the blood. The presence of the chlorides and the 

 alkaline sulphates assists in dissolving the sulphates, carbonates and the cal- 

 careous phosphates. The carbonates and phosphates are in part decomposed 

 in the system and furnish bases for certain of the organic salts, such as the 

 lactates, urates etc. 



2. Organic Saline Constituents. These substances are in greatest part 

 formed in the organism and they exist in the blood in very small quantity. 

 The lactates are probably produced by decomposition of a portion of the 

 bicarbonates and the union of the bases with lactic acid, the lactic acid 

 resulting, possibly, from a change of a portion of the saccharine matter in 

 the blood. The physiological relations of these substances are little under- 

 stood. The salts formed by the union of fatty acids with bases are probably 

 produced by decomposition of fatty matters, a great part of which is de- 

 rived from the food. 



3. Organic Non-nit rogenized Constituents. These usually exist in the 

 blood in small quantity and are derived mainly from the food. Lecethine, 

 although it contains nitrogen, is included in this class because it presents 

 many of the properties of the fats. It exists in the blood, bile, nerv- 

 ous substance and the yelk of egg. Its chemical properties and physio- 

 logical relations are not well understood. The saccharine matters and glyco- 

 gen are derived in part from the food and in part from the liver, where 

 glycogen is formed. They are of organic origin, definite chemical compo- 

 sition and crystallizable. The fats and sugars are distinguished from other 

 organic substances by the fact that they are composed of carbon, hydrogen 

 and oxygen. In the sugars, the hydrogen and oxygen exist in the propor- 

 tion to form water, which fact has given them the name of carbohydrates. 

 The constituents of this class play an 'important part in development and 

 nutrition. One of them, sugar, appears very early in foetal life, formed 

 first in the placenta and afterward in the liver, its formation by the lat- 

 ter organ continuing during life. Fat is a necessary constituent of food 

 and is also formed in the interior of the body. The exact influence which 

 these substances have on development and nutrition is not known ; but ex- 

 periments and observation have shown that this influence is important. 

 They will be considered more fully in connection with the physiology of 

 nutrition. 



4. Excrementitious Constituents. A full consideration of these sub- 

 stances, which are all formed by the process of disassimilation of the tissues 

 and are taken up by the blood to be eliminated by the proper organs, be- 



