EXCRETION 387 



and the total excretion by an average man of 70 kilos may 

 be given thus : 



Per 1000 grammes. In 24 hours. 



Water - 960 1440 grammes 



Solids .... 40 60 



Urea -23 35 x 



Uric acid and xanthin basest 075 I oramirpc 



Hippuricacid i8 o' 5 37 75 grammes. 



Kreatmin - 1-5 [ 



Sodium -\ 6 



Potassium - - 1 6'5 2*5 



Ammonia - - f 075 



Calcium and magnesium > o'5 ^22*25 grammes. 



Chlor'ne - -) 7 



Phosphoric acid - 8 3*5 



Sulphuric acid -J 2 



Mucus, p : gment, etc. 



The acidity of urine is not due to free acid, for the tests which 

 reveal the presence of free acid in a mixture, such as the precipitation 

 of sulphur on the addition of sodium hyposulphite, and the change 

 of colour of many organic substances, give a negative result when 

 applied to urine. The acidity is chiefly due to the acid phosphates 

 of sodium and potassium ; in a less degree to dissolved carbon 

 dioxide. That a considerable proportion of the phosphoric acid is 

 normally present in the form of acid sodium phosphate (NaH 2 PO 4 ) 

 is shown by the fact that barium chloride usually precipitates only 

 about 40 per cent, of the phosphoric acid, leaving the rest in solution. 

 Now, barium chloride does not cause a precipitate in a dilute solution 

 of acid sodium phosphate, but does precipitate the disodium-hydrogen 

 phosphate (Na 2 HPO 4 ). The acidity is estimated by running into a 

 given quantity of urine a dilute solution of sodium hydrate, which has 

 been previously titrated with a pure acid solution (say, oxalic acid) 

 of known strength, until a neutral reaction is just obtained. From 

 the amount of sodium hydrate required the acidity can be calculated 

 in terms of the standard acid. Normally the acidity of urine is about 

 equal to that of a o' i per cent, solution of sulphuric acid. It diminishes 

 distinctly, or even gives place to alkalinity, during digestion when 

 the acid of the gastric juice is being secreted, and varies with the 

 quantity of vegetable food in the diet. The urine of herbivora and 

 vegetarians is alkaline, and is either turbid when passed, or on stand- 

 ing soon becomes turbid from precipitated carbonates and phosphates 

 of earthy bases, while that of carnivora and of fasting herbivora, which 

 are living on their own tissues, is strongly acid and clear. Normal 

 human urine may deposit urates soon after discharge, as they are 

 more soluble in warm than in cold water. They carry down some 

 of the pigment, and therefore usually appear as a pink or brick-red 

 sediment. When urine is allowed to stand after being voided, what 

 is generally described as ' acid fermentation ' occurs. The acidity 

 gradually increases, owing apparently to the formation of lactic acid ; 

 acid sodium urate is produced from the neutral urate, and comes down 

 in the form of amorphous granules, while the liberated uric acid is 

 deposited often in 'whetstone ' crystals, coloured yellow by the pigment 



