120 HANDBOOK OF PHYSIOLOGY. 



other organic principle ; another part is important in regulating or modi- 

 fying various physical processes, as absorption, solution, and the like; 

 while a part must be reckoned only as matter, which is, so to speak, 

 accidentally present, whether derived from the food or the tissues, and 

 which will, at the first opportunity, be excreted from the body. 



Oases. The gaseous matters found in the body are Ox y yen, Hydro- 

 gen, Nitrogen, Carliiretted and Sulphuretted hydrogen, and Carbonic acid. 

 The first three have been referred to. Carburetted and sulphuretted 

 hydrogen are found in the intestinal canal. Carbonic acid is present in 

 the blood and other fluids, and is excreted in large quantities by the 

 lungs, and in very minute amount by the skin. It will be specially con- 

 sidered in the chapter on Eespiration. 



Water, the most abundant of the proximate principles, forms a large 

 proportion, more than two-thirds of the weight of the whole body. Its 

 relative amount in some of the principal solids and fluids of the body is 

 shown in the following table (from Bobiii and VerdeiPs) : 



QUANTITY OP WATER IN 1000 PARTS. 



. 880 



887 

 . 900 



936 

 . 960 



975 

 . 986 



995 



The importance of water as a constituent of the animal body may be 

 assumed from the preceding table, and is shown in a still more striking 

 manner by its withdrawal. If any tissue, as muscle, cartilage, or ten- 

 don, be subjected to heat sufficient to drive off the greater part of its 

 water, all its characteristic physical properties are destroyed ; and what 

 was previously soft, elastic, and flexible becomes hard and brittle, and 

 horny, so as to be scarcely recognizable. 



In all the fluids of the body blood, lymph, etc., water acts the 

 part of a general solvent, and by its means alone circulation of nutrient 

 matter is possible. It is the medium also in which all fluid and solid 

 aliments are dissolved before absorption, as well as the means by which 

 all, except gaseous, excretory products are removed. All the various 

 processes of secretion, transudation, and nutrition depend of necessity 

 on its presence for their performance. 



The greater part, by far, of the water present in the body is taken 

 into it as such from without, in the food and drink. A small amount, 

 however, is the result of the chemical union of hydrogen with oxygen in 

 the blood and tissue. The total amount taken into the body every day 



