Royal Society. 229 



ascertained that these tests are not to be relied upon, since indigo, 

 when contaminated (as in the urine it frequently is) with a large 

 quantity of animal matter, vibriones, &c, gives a reddish-brown so- 

 lution with concentrated sulphuric acid, from the charring of the 

 animal matter, and in many cases forms a bright blue solution with 

 boiling absolute alcohol ; hence he could not help suspecting that 

 cyanourine and indigo are very closely connected with each other, 

 if they be not identical. He observes, it is at least singular that 

 while so many cases of indigo were met with, not a single instance 

 of cyanourine presented itself. He also contrasts indigo with apo- 

 glaucine, and remarks that this is acknowledged by Heller himself to 

 be nothing more than cyanourine mixed with urrhodine. 



Taking then into consideration the whole of the facts described 

 in this communication, the following conclusions are deduced : — 



1st. That blue indigo is frequently formed in human urine, the 

 quantity being subject to the greatest variation ; in some cases it is 

 so considerable as to impart a deep green, or bluish-green colour 

 to the whole urine ; a pellicle of nearly pure indigo also extending 

 over the entire surface of the liquid ; while in others it is so small 

 that it can only be detected by means of the microscope. 



2nd. That for the formation of this indigo, it is in general neces- 

 sary that the urine should be exposed to the air for some days in an 

 open vessel, oxygen being absorbed and the blue indigo developed. 

 Whatever facilitates therefore oxygenation, as free exposure to light 

 and air, warmth and sunshine, hastens the appearance of the blue 

 indigo ; hence in summer the changes described take place much 

 more quickly than in winter ; on the contrary, these changes are re- 

 tarded and even stayed by exclusion of the atmosphere. Blue indigo 

 may even be deprived of its colour and reformed, alternately, accord- 

 ing as air is excluded or admitted to urine containing it. From some 

 of the cases recorded, it would appear, however, that blue indigo is 

 occasionally formed in the system, and is voided as such in the 

 urine. 



3rd. That there is usually found with the blue indigo, where the 

 amount of this is considerable, a brown extractive, sometimes in 

 large quantity, the aqueous solution of which, by exposure to air, 

 yields a further supply of coloured indigo, and which closely re- 

 sembles hsematinein its chemical manifestations and elementary com- 

 position. There is therefore great reason for believing that in the 

 majority of the cases here recorded, the blue indigo was derived 

 from altered heematine, although it is at the same time probable, that 

 in some cases it is formed from modified urine pigment which is 

 itself supposed to be a modification of hsematine. Between the greater 

 number of the animal colouring matters there is the closest relation- 

 ship in chemical composition, so that the transformation of the one 

 into the other would appear to be both easy and natural. 



4thly. That the urines in which the coloured indigo occurs in the 

 largest quantity, are usually of a pale straw colour, readily beco- 

 ming turbid, alkaline, and of low specific gravity. Small quantities 



