862 PHYSIOLOGY OF DIGESTION AND SECRETION. 



giving us phenolsulphuric acid(C 6 H50SO 2 OH), cresolsulphuric acid 

 (C 7 H 7 OS0 2 OH), indoxylsulphuric acid or indican (CgH^NOSOoOH), 

 and skatoxylsulphuric acid (C 9 H 8 NOSO 2 OH) . The indol, skatol, 

 phenol, and cresol are formed in the large intestine as a result of bac- 

 terial putrefaction. They are eliminated in part in the feces, but 

 in part are absorbed into the blood, and after oxidation are. 

 conjugated with sulphuric acid and eliminated in the urine. The 

 process of conjugation is valuable from a physiological standpoint, 

 as it converts substances having an injurious action into harmless 

 compounds. It should be added, also, that to a small extent the 

 phenol, indoxyl, and skatoxyl may be secreted in the urine as con- 

 jugated glucuronates, that is, in combination with glycuronic acid 

 (C 6 H 10 O 7 ), a reducing substance closely connected with dextrose. 

 From a nutritional standpoint the amount of these substances pres- 

 ent furnishes a measure of the extent of protein putrefaction in the 

 intestine, by virtue of the indol and phenol constituents. All con- 

 ditions that increase the putrefactive processes in the intestine 

 are accompanied by a parallel increase in the ethereal sulphates. 

 By virtue of the sulphuric acid component theee bodies represent 

 also one of the forms in which sulphur is excreted from the 

 body. (3) Some of the sulphur in the urine may occur in unoxid- 

 ized form as sulphocyanid or as ethyl-sulphide (Abel) ([C-jHJjS). 

 Under certain pathological conditions (cystinuria) some sulphur may 

 be excreted in the form of cystin, but this is not a normal con- 

 stituent of the urine. For other most interesting and significant 

 changes in the composition of the urine under pathological condi- 

 tions reference must be made to special works upon the urine or 

 upon pathological chemistry. 



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 quan- 

 tity 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, and there is some evidence (p. 849) that in 

 this case the excretion of the excess of water is controlled by a 

 special hormone found in the small intestine. The amount of 

 water secreted may be increased by the action of diuretics, such as 

 potassium nitrate and caffein. 



