340 -I.V AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



gram is excreted in twenty-tour hours. If, however, the diet is largely 

 table, tli is amount may be increased greatly. These last facts are readily 

 explained. It has been found that if benzoic acid or related substances con- 

 taining this group are fed to animals, they appear in the mine as hippuric 

 acid. Evidently, a synthesis has taken place within the body, and Bunge and 

 Schmiedeberg proved conclusively that in dogs, and probably, therefore, in 

 man, the union of the benzoic acid to glycocoll occurs mainly in the kidney 

 itself. We can understand, therefore, why vegetable foods which are known to 

 contain substances belonging to the aromatic series and yielding benzoic acid 

 should increase the output of hippuric acid in the urine. Since, however, in 

 starving animals or in animals \\<\ entirely on meat hippuric acid is still pres- 

 ent, although reduced in amount, it follows that it arises in part as one of the 

 results of body-metabolism. Among the various products of the breaking- 

 down of the proteid molecule, it is probable that some benzoic acid occurs, 

 and, if so, it is excreted in combination with glycocoll as hippuric acid. It 

 should lie added, finally, that some of the hippuric acid is supposed to be de- 

 rived from the process of proteid putrefaction that occurs to a greater or 

 less extent in the large intestine. 



Conjugated Sulphates. — A good part of the sulphur eliminated in the 

 urine is in the form of ethereal salts with organic compounds of the aromatic 

 and indigo series. Quite a number of these compounds have been described ; 

 the most important are the compounds with phenol (C 6 H 5 OS0 2 OH), cresol 

 (C 7 H 7 O.S0 2 OH), indol (C s H 6 XOS0 2 OH), and skatol (C 9 H 8 XOS0 2 OH). 

 These four substances, phenol, cresol, indol, and skatol, are formed in the in- 

 testine during the process of putrefactive decomposition of the proteids (p. 310). 

 They are produced in small quantities, and they may be excreted in part in 

 the feces, but in part they are absorbed into the blood. They are in them- 

 selves injurious substances, but it is supposed that in passing through the 

 liver — which must of necessity happen before they get into the general cir- 

 culation — they are synthetically combined with sulphuric acid, making the 

 so-called "conjugated sulphates," which are harmless, and which are event- 

 ually excreted by the kidneys. 



Water and Inorganic Salts. — Water is lost from the body through three 

 main channels — namely, the lungs, the skin, and the kidney, the last of these 

 being the most important. The quantity of water lost through the lungs 

 probably varies within small limits only. The quantity lost through the 

 sweat varies, of course, with the temperature, with exercise, etc., and it may 

 be said that the amounts of water secreted through kidney and skin stand in 

 something of an inverse proportion to each other; that is, the greater the 

 quantity lost through the skin, the less will be secreted by the kidneys. 

 Through these three organs, but mainly through the kidneys, the blood is 

 being continually depleted of water, and the loss must be made up by the 

 ingestion of new water. When water is swallowed in excess the superfluous 

 amount is rapidly eliminated through the kidneys. The amount of water 



