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ter found was very considerable, in others less; and in the third 

 class of cases the microscope was necessary for its discovery. In 

 nearly all these cases the blue colouring matter was submitted to 

 analysis, and ascertained, on the clearest evidence, to be indigo. 



The author in the next place considers the question of the source 

 and origin of indigo in the urine. 



it appeared that in the cases related by the author, coloured 

 indigo was not present in urine when first voided, but that it was 

 gradually formed some time afterwards by a process of oxidation on 

 exposure to the air, being in most of the cases probably derived from 

 the brown extractive, which in its chemical manifestations so closely 

 resembles hsematin. 



The author contrasts cyanourine with the indigo detected in urine. 

 He observes that the most distinctive tests laid down for cyanourine 

 are its solubility in boiling alcohol, and the action of sulphuric acid 

 upon it, which give a reddish-brown solution ; and states he had 

 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- 

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

 be nothing more than cyanourine mixed with urrhodin. 



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 biuish-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 



