408 PHYSIOLOGY CHAP. 



about 20 per cent of the total sulphur. It consists partly of the 

 sulphocyanide^ of the saliva, partly of the taurine of the bile, partly 

 of compounds homologous with cystine. 



Phosphoric acid is present in normal urine, in the form of 

 alkaline phosphates (mostly sodium, a little potassium) and of 

 earthy phosphates (chiefly calcium, a very little magnesium). 



The acidity of the urine, as stated, depends principally on the 

 monobasic phosphates of sodium and calcium, the so-called acid 

 phosphates. When the urine is neutral, part of the monobasic are 

 replaced by dibasic phosphates. When, lastly, the urine is alkaline, 

 a more or less considerable part of the phosphates is found in the 

 form of tribasic phosphate, sodium, calcium, magnesium. Lastly, 

 it should be noted that part of the phosphoric acid in the urine is 

 combined with ammonia. 



The phosphoric acid of the urine comes partly from the food, 

 partly from the decomposition of the organic phosphorus com- 

 pounds of the tissues. Meat, milk, cereals, vegetables, which 

 represent the principal food -stuffs, are more or less rich in 

 phosphates. Part, however, of these alimentary phosphates 

 (particularly the phosphates of calcium and magnesium) are not 

 absorbed by the intestine, but pass out unaltered in the faeces. 



In fact the urine of herbivora is comparatively poor in phos- 

 phates, although earthy phosphates abound in their diet. But 

 the tissues are also more or less rich in phosphates, the bones 

 especially so in the form of calcium and magnesium phosphate. 

 There is, further, a group of organic phosphorus compounds, in 

 which are included the nuclein, which forms the chromatin of cell 

 nuclei, lecithin, which is most plentiful in the nervous system, and 

 jecorin, found principally in the liver. All these substances are 

 able by oxidation of the phosphorus to form phosphoric acid which 

 appears in the urine. 



The amount of phosphoric acid excreted daily fluctuat 

 between 2'5 and 3'5 grms. The earthy phosphates represent 

 about half the total phosphates. In general it may be stated that 

 the fluctuations of the phosphorus content of the urine correspond 

 with the fluctuations of the nitrogen content. This is especially 

 shown when the subject experimented on is kept on a constant 

 diet, so that the amount of phosphates and inorganic phosphorv 

 compounds introduced does not vary perceptibly. On a normal 

 mixed diet, the average ratio between the phosphorus and nitrogen 

 content of the urine is as 1 : 17'45, i.e. for one gramme of phos- 

 phorus there are 17'45 grammes nitrogen in the urine. During 



Succi's 30 days' fast at Florence, we found that the quotient p w 



always lower than 17'45, which means that during inanition the 

 excretion of phosphorus increases considerably in comparison with 

 the excretion of nitrogen. I. Munk made the same observation 



