374: EXCRETION BY THE SKIN AND KIDNEYS. 



years of age, to be fifty-two and a half fluidounces (1,552-6 c. c.), the average 

 quantity per hour being two and one-tenth fluidounces (62 c. c.). The 

 extremes were thirty-five ounces and eighty-one ounces (1,035 and 2,395 

 c. c.). The average quantity may be assumed to be about fifty-one fluid- 

 ounces (1,500 c. c.). The normal range of variation is between thirty and 

 sixty ounces (about 900 and 1,775 c. c.). The conditions which lead to a 

 diminution in the quantity of urine usually are more efficient in their opera- 

 tion than those which tend to an increase ; and the range below the normal 

 standard is rather wider than it is above. More urine usually is secreted 

 during the day than at night. The quantity of water discharged by the 

 kidneys in the twenty-four hours is a little greater in the female than in the 

 male ; but in the female the specific gravity is lower, and the quantity of solid 

 constituents is relatively and absolutely less (Becquerel). 



The specific gravity of the urine should be estimated in connection with 

 the absolute quantity in the twenty-four hours. Those who assume that the 

 daily quantity is about fifty-one ounces (1,500 c. c.), give the ordinary specific 

 gravity of the mixed urine of the twenty-four hours as about 1020. The 

 specific gravity is liable to the same variations as the proportion of water, and 

 the density is increased as the water is diminished. The ordinary range 

 variation in specific gravity is between 1015 and 1025 ; but without positivelj 

 indicating any pathological condition, it may be as low as 1005 or as higl 

 as 1030. 



The reaction of the urine is acid in the carnivora and alkaline in th 

 herbivora. In the human subject it usually is acid at the moment of it 

 discharge from the bladder; although at certain times of the day it ma) 

 be neutral or feebly alkaline, the reaction depending upon the charact 

 of the food. The acidity may be measured by neutralizing the urine wit 

 an alkali in a solution that has previously been graduated with a solution 

 of oxalic acid of known strength ; and the degree of acidity is usually ex- 

 pressed by calling it equivalent to so many grains of crystallized oxalic 

 acid. 



As the result of a large number of observations made by Vogel and under 

 his direction, the total quantity of acid in the urine of the twenty-four hours 

 in a healthy adult male is equal to between thirty and sixty grains (2 and 4 

 grammes) of oxalic acid. The hourly quantity in these observations \vas 

 equal, in round numbers, to between one and a half and three grains (0*1 and 

 0-2 gramme) of acid. The proportion of acid was found to be very variable 

 in the same person at different times of the day. The urine contains no free 

 acid, but its acidity under an animal or a mixed diet depends upon the pres- 

 ence of acid salts, of which the principal one is acid sodium phosphate, with 

 possibly a little acid calcium phosphate. 



Composition of the Urine. Kegarding the excrementitious constituents 

 of the urine as a measure, to a certain extent, of the general process of dis- 

 similation, it is more important to recognize the quantities of these products 

 discharged in a definite time than to learn simply their proportions in the 

 urine ; and in the following table of composition of the urine, the absolute 



