254 LECTURE XII. 



occurs before the latter has been oxidized to sulphuric acid. It is very 

 probable that the final oxidation to sulphuric acid only takes place after 

 the substances have united. We must not neglect to call attention to the 

 analogy existing between the formation of the sulphuric acid compounds 

 and the conjugated glucuronic acids. The latter are also of secondary 

 nature, only appearing after the dextrose has combined with some of the 

 conjugating substance. 1 



We shall now consider those compounds which are produced by the 

 aromatic cleavage substances of proteins being conjugated with sulphuric 

 acid. Let us consider first of all phenylsulphuric acid: 



C 6 H 5 O . S0 2 . OH 

 and the p-tolyl sulphuric acid: 



C 6 H 4 



Both have the same origin and are always classed together. They are 

 found in urine as alkali salts. The quantity of each varies, and depends, 

 as can easily be imagined, on the intensity of the intestinal putrefaction 

 and the amount of resulting products that is absorbed. Tyrosine is the 

 mother-substance of the phenols. As we have seen, all the phenol admin- 

 istered to the body is not excreted as such combined with sulphuric acid 

 in the urine. A part is changed in another way, probably consumed, while 

 another portion is in some cases found in the urine, oxidized to quinoyl- 

 sulphuric acid. This cannot be detected under normal conditions, although 

 catechoylsulphuric acid is often present in urine, if only in small amount. 

 Catechol is o-dihydroxybenzene. It has never been definitely decided 

 whether its sulphuric acid ester is produced by the oxidation of phenol, 

 or arises from some constituent in the food which is not directly related 

 to the proteins. 



There is some evidence indicating that catechoylsulphuric acid results 

 from a vegetarian diet, but is not formed in a diet exclusively of meat. It 

 has been suggested that protocatechuic acid is the mother-substance of 

 the sulphuric acid ester mentioned. 



We will add to the phenyl- and tolylsulphuric acids the other decom- 

 position products of tyrosine which occur in urine. They may be con- 

 sidered as intermediate products between tyrosine and phenol. Thus, 

 there has been found in urine: p-hydroxyphenylpropionic acid (p-hydro- 

 cumaric acid) : ^j^ ^ QH ^ ^ ^ ^ ^ COQHj 



and the p-hydroxyphenylacetic acid: 2 



C 6 H 4 . OH . CH 2 . COOH. 



1 Cf. Lecture II, p. 33. 



3 E. Baumann: Z. physiol. Chem. 4, 304 (1880); 6, 183 and 234 (1882). 



