EXCRETION OF MATTER FROM THE BODY 399 

 4. Hippuric Acid. This is benz-amido-acetic acid. 



H 



H 



_C C H 

 H 



It is formed from benzoic acid taken in the food by link- 

 ing it to glycocoll amido-acetic acid. This synthesis appears 

 to take place in the kidneys, for it has been found that 

 hippuric acid is not formed when these organs are excised, 

 and that, when blood containing benzoates is circulated 

 through them, hippuric acid is produced. Its chief interest 

 is in the fact that it is one of the first organic compounds 

 which were demonstrated to be formed synthetically in the 

 animal body. Normally it is present in human urine in 

 very small quantities, but in the urine of herbivora the 

 amount is considerable, from the presence of benzoic acid 

 in the fodder. The acid itself is insoluble, and it occurs as 

 the soluble soda salts. 



II. Sulphur-containing Bodies. 



The sulphur excreted in the urine is derived from the 

 sulphur of the proteid molecule, and the amount of sulphur 

 excreted may be taken as a measure of the amount of pro- 

 teid decomposed. This is sometimes used as a check upon 

 an estimation from the excretion of nitrogen. 



A. Acid Sulphur. The greater part of the sulphur is 

 fully oxidised to S0 3 . (a) Preformed Sulphates. About 

 nine-tenths of this is linked with bases to form ordinary 

 sulphates. 



(b) The other one-tenth is in organic combination, linked 

 to benzene compounds, Ethereal Sulphates. The indol, 

 skatol, and phenol (see p. 351), formed by the putrefaction 

 of proteids in the bowel, being excreted in the urine in an 

 oxidised form linked with sulphuric acid. Indol, as already 

 shown, is related to amido-ethyl-benzene. 



