264 THE URINE. 



which was not used in the formation of tri-iodophenol, retitrated with 

 a decinormal solution of sodium thiosulphate. One c.c. of the iodine 

 solution represents 1.567 milligramme of phenol, or 1.8018 milli- 

 gramme of cresol. As the latter predominates in the urine, it is best 

 to express the results in terms of cresol. Thus modified, the method 

 is also applicable in the presence of sugar. The older gravimetric 

 method, by which the phenols were isolated as bromine substitution- 

 products, has now been largely abandoned, as it has been shown 

 that the resulting precipitate is not of constant composition, and 

 contains variable amounts of dibromocresol, besides tribromophenol 

 and bromo-tribromophenol. 



Indoxyl Sulphate. The indoxyl sulphate which occurs in the 

 urine in combination with potassium and sodium is usually spoken 

 of as indican, but should not be confounded with vegetable indican, 

 which is a glucoside of the composition C 26 H 31 NO 17 . The amount 

 which is daily excreted by man is normally small, and corresponds 

 to about 0.0066 gramme. Larger quantities are observed when 

 from any cause intestinal putrefaction is increased, or in cases in 

 which putrefactive changes are taking place in the body proper, as 

 in empyema, providing that active resorption can occur. 



In herbivorous animals larger amounts are found than in the 

 carnivora. Artificially an increased elimination can be effected by 

 feeding animals with ortho-nitro-phenyl-propiolic acid, which is 

 reduced in the body to indoxyl, according to the equation : 



/C=COOH /C.OH=CH 



+ OTT (~\ TT / I OTT (~\ 



OXl V^gilX }- O1^\J 



Ortho-nitro-phenyl- Indoxyl. 



propiolic acid. 



Indican crystallizes in colorless platelets, which are readily soluble 

 in water and hot alcohol, while in cold alcohol they dissolve with 

 great difficulty. On decomposition with hydrochloric acid the 

 indoxyl is obtained in the form of oily droplets of an exceedingly 

 offensive, feculent odor. On oxidation this is then transformed into 

 indigo-blue, as is shown in the equation : 



C.OH = CH CO v 



Indoxyl. Indigo-blue. 



On heating an aqueous solution of indoxyl to a temperature 

 of 130 C. indoxyl-red results. This is a brown amorphous sub- 

 stance, which is insoluble in water, but dissolves with ease in 

 alcohol, ether, and chloroform, with a beautiful red color. When 

 Jaffe's test for indican is applied to the urine, or when this is boiled 

 and treated drop by drop with concentrated nitric acid (Rosenbach's 

 reaction), a mixture of a blue and a red pigment is not infrequently 

 obtained, and it is quite likely that the latter is in part at least refer- 

 able to the formation of the indoxyl-red. According to some observ- 



