186/.] 



Extractive Matters of Urine.—V^vt I. 



89 



substance, having an acid reaction, insoluble in water, but soluble in alcoliol, 

 and which he supposed must exist in the secretion in a free state. I have 

 uo doubt, however, that this and all similar bodies are products of decom- 

 position derived from the extractive matters or the indigo-producing sub- 

 stance of the urine. They do not preexist in the secretion, but are formed 

 during the process of preparation by the action of the reagents employed. 

 Even a prolonged heating at 100° C. is quite sufficient, as I shall hereafter 

 show, to produce a complete decomposition of the extractive matters, and 

 their conversion into products of an entirely different nature, consisting in 

 great part of brown resinous substances insoluble in water. 



The investigations touching this subject which remain to be noticed are 

 few in number. Notwithstanding its importance from a physiological point 

 of view, the difficulties connected with it, and the uncertainty of the con- 

 clusions to which most previous researches had led, probably deterred many 

 from enterins; on its investia-ation. Tichborne's * account of the normal 

 urinary pigment differs from those of some of his predecessors. According 

 to him the colouring-matter of normal urine is a brovrn, amorphous sub- 

 stance, which is very hygroscopic, easily soluble in water, less soluble in 

 alcohol, and insoluble in ether. The colour of its watery solution cannot 

 be distinguished from that of ordinary urine, and by making it more or 

 less dilute, the several tints of normal urine miay be imitated. Tichborne 

 has given the results of its analysis, which is probably the first ever made 

 of any urinary extractive matter, that is, of the substance as it exists in 

 urine to which the usual colour of the secretion is due. His results, how- 

 ever, differ very widely from those arrived at by myself, and lead to a com- 

 position more nearly approaching that of the brown colouring-matters 

 insoluble in water so often obtained in previous experiments. The hypo- 

 thesis which he has ventured to set up, viz. that this substance is derived 

 in some way from hippuric acid, is, I think, totally without foundation. 

 Indeed there are more reasons in favour of the converse hypothesis, viz. 

 that the urinary extractive matters are the source, or at least one source, of 

 hippuric acid. The existence in urine of more than one kind of extractive 

 matter seems to have escaped the notice of this observer. 



By far the most complete investigation of the colouring-matters of normal 

 urine is that of Dr. Tliudichum f . The results of this investigation having 

 quite recently been made known, I need not enter at present into any of 

 the details. In giving an account of my own experiments, I shall have oc- 

 casion to show that my results differ in many respects from those of Dr^ 

 Thudichum. I cannot, however, even now refrain from expressing my sur- 

 prise that, notwithstanding the numerous observations and experiments of 

 chemists on the blue and red colouring-matters from urine, he should have 

 arrived at the conclusion that " from healthy human urine neither indican 

 nor uroxanthine, nor any other substance yielding, by decomposition with 



^ Chemical News, vol. v. p. 171. 

 t British Medical Journal, Novoniber 5, 18G4. 

 VOL. XYI. II 



