72 MANUAL OF PHYSIOLOGY. 



entire body-weight. The amount in each texture varies, and thus 

 the different tissues have widely different consistence. 



Water is introduced into the body in all kinds of drink, and a 

 large quantity is also taken with our solid food. It is highly 

 probable, that in the chemical changes which take place in the 

 tissues, some water is formed by the oxidization of the hydrogen 

 of the more complex substances. 



In the economy it acts as the universal solvent in the fluids of 

 the body, and as the agent by means of which the chemical changes 

 of the various organs are enabled to be accomplished. 



The water leaves the body by the lungs as vapor, and by the 

 skin, kidney, and many other glands, as the fluid in which their 

 secretions are dissolved. 



Inorganic acids occur either combined to form salts, in which 

 condition we find several in the body (sulphuric, phosphoric, sili- 

 cic), or uncombined. In the latter state we have only two, viz.: 



Hydrochloric Acid, HC1, which is manufactured by the mucous 

 membrane of the stomach, and takes an important part in gastric 

 digestion. 



Carbonic Acid Gas, CO 2 , exists in most of the fluids of the body, 

 having been absorbed by them from the tissues during their com- 

 bustion. The venous blood contains a considerable quantity, which 

 is got rid of during the passage of the blood through the lungs. 

 It is distinctly a waste product, that must be constantly eliminated 

 from the body (see Respiration). 



A large number of salts occur in the tissues, generally in small 

 quantity, in solution. In the teeth and in bone tissue salts exist 

 in the solid form, and in much greater proportion than in any of 

 the soft parts. Most of the salts are introduced into the economy 

 with the food, but some, doubtless, are formed in the body itself. 

 Our knowledge of the exact position occupied by the salts in the 

 textures is very incomplete, as their amount is only estimated from 

 the ash of the tissue which remains after ignition, by which pro- 

 cess they become altered, so that it is impossible to say what are 

 the exact salts that are present in the body. They doubtless form 

 chemical combination! with the complex organic compounds, 

 which we do not understand, and probably have important func- 

 tions to perform, such as rendering certain materials (globulins) 



