REACTIONS OF THE URINE. 355 



of decomposing the iodide of starch, after it has once been formed. 

 This peculiar action of the urine was first noticed and described 

 by us in 1856. 1 If 3j of iodine water be mixed with a solution 

 of starch, it strikes an opaq ue blue color ; but if 3j of fresh urine 

 be afterward added to the mixture, the color is entirely destroyed 

 at the end of four or five seconds. If fresh urine be mixed with 

 four or five times its volume of iodine water, and starch be 

 subsequently added, no union takes place between the starch and 

 iodine, and no blue color is produced. In these instances, the iodine 

 unites with the animal matters of the urine in preference to com- 

 bining with the starch, and is consequently prevented from striking 

 its ordinary blue color with the latter. This interference occurs 

 whether the urine be acid or alkaline in reaction. In all cases in 

 which iodine exists in the urine, as for example where it has been 

 administered as a medicine, it is under the form of an organic com- 

 bination ; and in order to detect its presence by means of starch, a 

 few drops of nitric acid must be added at the same time, so as to 

 destroy the organic matters, after which the blue color immediately 

 appears, if iodine be present. This reaction with starch and iodine 

 belongs also, to some extent, to most of the other animal fluids, as 

 the saliva, gastric and pancreatic juices, serum of the blood, &c. ; 

 but it is most strongly marked in the urine. 



Another remarkable property of the urine, also dependent on its 

 organic ingredients, is that of interfering with Trommer's test for 

 grape sugar. If clarified honey be mixed with fresh urine, and sul- 

 phate of copper with an excess of potassa be afterward added, the 

 mixture takes a dingy, grayish-blue color. On boiling, the color 

 turns yellowish or yellowish-brown, but the suboxide of copper is 

 not deposited. In order to remove the organic matter and detect 

 the sugar, the urine must be first treated with an excess of animal 

 charcoal and filtered. By this means the organic substances are 

 retained upon the filter, while the sugar passes through in solution, 

 and may then be detected as usual by Trommer's test. 



ACCIDENTAL INGREDIENTS OF THE URINE. Since the urine, in 

 its natural state, consists of materials which are already prepared in 

 the blood, and which merely pass out through the kidneys by a 

 kind of filtration, it is not surprising that most medicinal and 

 poisonous substances, introduced into the circulation, should be 



1 American Journal Me<l. Sci., April, 1S56. 



