386 EXCRETION BY THE SKIN AND KIDNEYS. 



deed, it has been shown by direct observations that this is the fact. The pro- 

 portion of sodium chloride in the blood seems to be tolerably constant ; and 

 any excess that may be introduced is thrown off, chiefly by the kidneys. As 

 the chlorides are deposited with the organic matters in all the acts of nutri- 

 tion, they are found to be eliminated constantly with the products of dis- 

 assimilation of the nitrogenized parts, and their absence from the food does 

 not completely arrest their discharge in the urine. According to Robin, by 

 suppressing salt in the food, its daily excretion may be reduced to between 

 thirty and forty-five grains (1-9 and 2-9 grammes). This quantity is less 

 than that ordinarily contained in the ingesta, and under these conditions 

 there is a gradual diminution in the general nutritive activity. In nearly all 

 acute febrile disorders the chlorine in the urine rapidly diminishes and is 

 frequently reduced to one-hundredth of the normal proportion. The quan- 

 tity rapidly increases to the normal standard during convalescence. Most of 

 the chlorides of the urine are in simple watery solution ; but a certain pro - 

 portion of sodium chloride exists in combination with urea. 



The daily elimination of sodium chloride is about one hundred and fifty- 

 four grains (10 grammes.) The great variations in its proportion in the 

 urine, under different conditions of alimentation, etc., will explain the differ- 

 ences in the estimates given by various authorities. 



Sulphates. There is very little to be said regarding the sulphates, in 

 addition to the general statements already made concerning the inorganic 

 constituents of the urine. The proportion of these salts in the urine is very 

 much greater than in the blood, in which there exist only about 0-28 of a, 

 'part per thousand. Inasmuch as the proportion in the urine is three to 

 seven parts per thousand, it seems probable that the kidneys eliminate these 

 salts as fast as they find their way into the circulating fluid either from the 

 food or from the tissues. Like other constituents derived in great part from 

 the food, the normal variations in the proportion of sulphates in the urine 

 are very great. It is unnecessary to consider in detail the variations in the 

 quantity of sulphates discharged in the urine, depending upon the ingestion 

 of different salts or upon diet, for all recorded observations have given the 

 same results, and they show that the ingestion of sulphates in quantity is 

 followed by a corresponding increase in the proportion eliminated. 



Thudichum estimated the daily excretion of sulphuric acid at 23 to 38 

 grains (1-5 to 2-5 grammes). Assuming that the sulphates consist of about 

 equal parts of potassium sulphate and sodium sulphate with traces of calcium 

 sulphate, the quantity of salts would be 22'5 to 37'5 grains (1-46 to 2-23 

 grammes) of potassium sulphate, with an equal quantity of sodium sul- 

 phate. 



Phosphates. The urine contains phosphates in a variety of forms ; but 

 inasmuch as it is not known that any one of the different combinations pos- 

 sesses peculiar relations to the processes of disassimilation, as distinguished 

 from the other phosphates, the phosphatic salts may be considered together. 



The phosphates exist constantly in the urine and are derived in part from 

 the food and in part from the tissues. Like other inorganic matters, they are 



