280 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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 OSO 2 OH), cresol 

 (C 7 H 7 O.S0 2 OH), indol (C 8 H 6 NOSO 2 OH), and skatol (C 9 H 8 NOSO 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. 249). 

 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 in passing through the liver which must of 

 necessity happen before they get into the general circulation they are syn- 

 thetically combined with sulphuric acid, making the so-called " conjugated sul- 

 phates," which are harmless, and which are eventually 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 

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

 and caffein, which probably act directly upon the secretory cells in the 

 glomeruli. 



The inorganic salts of urine consist chiefly of the chlorides, phosphates, 

 and sulphates of the alkalies and the alkaline earths. It may be said in gen- 

 eral that they arise partly from the salts ingested with the food, which salts 

 are eliminated from the blood by the kidney in the water-secretion, and in part 

 they are formed in the destructive metabolism which takes place in the body, 

 particularly that involving the proteids and related bodies. Sodium chloride 

 occurs in the largest quantities, averaging about 15 grams per day, of which 

 the larger part, doubtless, is derived directly from the salt taken in the food. 

 The phosphates occur in combination with Ca and Mg, but chiefly as the acid 

 phosphates of Na or K. The acid reaction of the urine is caused by these 

 latter substances. The phosphates come in part from the destruction of phos- 

 phorus-containing tissues in the body, but chiefly from the phosphates of the 

 food. The sulphates of urine are found partly conjugated with organic sub- 

 stances, as described above, and partly as simple sulphates. The total quantity 

 of sulphuric acid eliminated is estimated to average about 2.5 grams per day. 

 Sulphur constitutes a constant element of the proteid molecule, and the quan- 

 tity of it eliminated in the urine may be used, as in the case of nitrogen, to 

 determine the total destruction of proteid within a given period. 



