80 



Mi\ E. Sclmnck on the CGlouring and 



[Recess^ 



stance separates, mostly at the surface, but partly at the bottom. If the 

 flask, while still closed, be shaken, scarcely any change of colour takes 

 place ; but if it be shaken after the stopper has been removed and air ad- 

 mitted, the urine becomes, by shaking Avith the air, more or less green, 

 often very beautifully grass-green. On standing it again becomes pale, and 

 these appearances may be repeated at pleasure with urine that has been 

 kept for months in a flask. This phenomenon, viz., that a strongly 

 alkaline urine containing the mixture of colouring- matters only becomes 

 green by contact with air and not as long as the vessel is closed, is one the 

 cause of which I have not as yet been able to ascertain." Any one 

 acquainted with the properties of indigo-blue would, however, have under- 

 stood the matter at once. By the combined action of the alkali and the 

 deoxidizing matters contained in the urine, the indigo-blue in Heller's ex- 

 periment was reduced and dissolved, forming a true indigo- vat, and on 

 admitting air it vi?as reoxidized and precipitated, to be dissolved again when 

 the vessel was closed. Several years later H. v. Sicherer* obtained from 

 a specimen of m.orbid urine, by the action of strong acids, a blue deposit, 

 the properties of which he found to be those of indigo-blue. 



Heller's experiments were followed, after an interval of some years, by 

 those of Hassall f , who observed the formation of a blue colouring-matter 

 on allowing urine from disease to stand for some time exposed to the air. 

 The colouring-matter was mixed with phosphates, mucus, and other im- 

 purities ; but after the latter had been, as far as possible, removed, it was 

 found to consist of indigo -blue. Hassall inferred from his experiments 

 that the occurrence of this substance in the urine is strictly pathological. 

 *'"\Ye should be led," he says, *'to look for its occurrence in the urine in 

 all those cases of functional derangement of any kind in which any impedi- 

 ment exists to decarbonization, as is the case especially in most diseases of 



the organs of respiration It does not appear that, by any treatment 



of the urine with reagents, indigo can be developed in healthy urine at will. 

 I have made several attempts with this view, but without obtaining any 

 definite result." This opinion proved, however, to be erroneous. 



This subject was next taken up by myself J. My experiments on the 

 formation of indigo-blue in plants yielding that colouring-matter led to the 

 conclusion that these plants contain a peculiar substance, belonging to the 

 class of glucosides, which I named indican. As this substance is easily 

 soluble in water, alcohol, and ether, and yields, by decomposition with 

 acids, indigo-blue and sugar, I thought it probable that the formation of 

 indigo-blue in urine might be due to the presence of a similar body in the 

 secretion. This supposition was found to be correct. Not being able to 

 procure specim.ens of morbid urine such as would be hkely to yield the 

 colouring-matter, I was compelled to employ healthy urine ; but after de- 



* Annalen der Chem. unci Pharm., B. xc. S. 120. 

 t Philosophical Transactions, 1854, p. 297. 



X Memoirs of the Literary and Philosophical Society of Manchester, vol. xiv. p. 2o9. 



