PROTEIN METABOLISM 869 



SULPHUR 



Sulphur occurs in the urine in three forms, namely, as ordinary 

 inorganic sulphates, as ethereal sulphates (indoxy- and skatoxy-sul- 

 phates), and in an unoxidised condition often termed neutral sulphur. 

 There is no doubt that part of the latter consists of cystine, part of 

 sulphocyanates, and in some animals mercaptan compounds. The 

 excretion of the inorganic sulphates rises pari passu with that of the 

 urea, so that very soon after the throwing off of the NH 2 group there 

 must be also a removal and oxidation of the greater part of the sulphur 

 contained in the cystine. group of the protein molecule. So far as 

 regards the metabolism of the body as a whole, the ethereal sulphates 

 may be classed with the inorganic sulphates. They are excreted in 

 varying quantity according to the extent of the decomposition pro- 

 cesses which are occurring in the intestine. Under the influence of 

 these processes the tryptophane, produced in the pancreatic digestion 

 of proteins, is converted into indol and skatol. These two substances 

 after absorption are deprived of their poisonous qualities by oxidation 

 and conjugation with sulphuric acid to form the indoxy- and skatoxy- 

 sulphates of the urine, both of which are innocuous. If the processes 

 of putrefaction are increased, as in intestinal obstruction, the relative 

 amount of sulphate appearing in the conjugated form is also increased. 

 On administration of phenol a large proportion of the sulphate appears 

 in the urine conjugated with phenol or with products of its oxidation. 

 If the normal putrefactive processes which go on in the intestine are 

 abolished by the administration of intestinal antiseptics such as 

 naphthalene or calomel, the ethereal sulphates practically disappear 

 from the urine. We cannot therefore regard the absence or diminution 

 in the ethereal sulphates during protein starvation as throwing any 

 light on the endogenous protein metabolism. On the other hand, the 

 fact that the neutral sulphur undergoes no decrease suggests that this 

 part of the sulphur output of the organism may be connected with 

 tissue metabolism. Further observations on tlj.e output of neutral 

 sulphur during fever or wasting diseases are necessary before a 

 definite conclusion can be arrived at on this point. 



THE FATE OF THE AROMATIC AND OTHER CYCLIC 



GROUPS IN THE PROTEIN MOLECULE 



A typical protein such as can be utilised as a complete food-stuff 

 contains, in addition to the amino-acids of the fatty series, a number 

 of other nitrogenous derivatives of cyclic compounds, including 

 benzene, indol, pyrrol, and iminazol. Substances such as gelatin, from 

 which some of these groupings are absent, cannot, as we have seen, 



