378 EXCRETION BY THE SKIN AND KIDNEYS. 



to any great extent in the chlorides. The results of experiments upon this 

 point seem to show that water taken in excess increases the activity of disas- 

 similation. 



The ordinary meals increase the solid constituents of the urine, the most 

 constant and uniform increase being in the proportion of urea. This, how- 

 ever, depends to a great extent upon the kind of food taken. The increase 

 is usually noted during the first hour after a meal, and it attains its maxi- 

 mum at the third or fourth hour. The inorganic matters are increased as 

 well as the excremehtitious substances proper. The urine passed after food, 

 has been called urina cibi, under the idea that it is to be distinguished from 

 the urine supposed to be derived exclusively from disassimilation of the tis- 

 sues, which is called the urina sanguinis. 



It is an important question, to determine the influence of different kinds 

 of food upon the composition of the urine, particularly the comparative 

 effects of a nitrogenized and a non-nitrogenized diet. Lehmann has made a 

 number of observations upon this point, and his results have been confirmed 

 by many other physiologists. Without discussing fully all of these observa- 

 tions, it is sufficient to state that the ingestion of an excess of nitrogenized 

 food always produced a great increase in the proportion of the nitrogenized 

 constituents of the urine, particularly the urea, On a non-nitrogenized diet, 

 the proportion of urea was found to be diminished more than one-half. The 

 general results of the experiments of Lehmann are embodied in the following 

 quotation : 



" My experiments show that the amount of urea which is excreted is ex- 

 tremely dependent on the nature of the food which has been previously taken. 

 On a purely animal diet, or on food very rich in nitrogen, there were often 

 two-fifths more urea excreted than on a mixed diet ; while, on a mixed diet, 

 there was almost one-third more than on a purely vegetable diet; while, 

 finally, on a non-nitrogenous diet, the amount of urea was less than half the 

 quantity excreted during an ordinary mixed diet." 



The influence of food is not absolutely confined to the period when any 

 particular kind of food is taken, but is continued for many hours after a re- 

 turn to the ordinary diet. 



With regard to the influence of food upon the inorganic constituents of 

 the urine, it may be stated in general terms that the ingestion of mineral 

 substances increases their proportion in the excretions. 



There are certain articles which, when taken into the system, the diet 

 being regular, seem to retard the process of disassimilation ; or at least they 

 diminish, in a marked manner, the quantity of matters excreted, particularly 

 urea. Alcohol has a very decided influence of this kind. Its action may be 

 modified by the presence of salts and other matters in the different alcoholic 

 beverages, but in nearly all direct experiments, alcohol either taken under 

 normal conditions of diet, when the diet is deficient or when it is in excess, 

 diminishes the excretion of urea. The same may be stated in general terms 

 of tea and coffee. 



Influence of Muscular Exercise upon the Elimination of Nitrogen. In 



