AMOUNT AND COMPOSITION OF THE URINE 565 



a potassium salt. The test for indican in the urine consists in oxidiz- 

 ing the indoxyl in an acid solution by means of ferric chloride to indigo 

 blue, and shaking out the indigo blue with chloroform. The depth of 

 the color of the chloroform affords a rough means of determining 

 the amount of indican present. The fact that the indican test is nega- 

 tive must not be taken to mean that the intestinal processes are normal, 

 for if the intestine fails to contain phenylated amino acids, or the proper 

 bacteria are not present, no indican will be found. On the other hand, 

 the putrefactive process of the large bowel may not be very extensive, 

 yet the amount of indican in the urine be increased, because of greater 

 absorption due to constipation. 



Skatole, ajejsaLsmetHng substance, is formed by certain kinds of bac- 

 teria. The greater proportion of this substance is excreted by the bowel, 

 but if the person is constipated, some of it may find its way into the 

 blood to impart a fecal odor to the breath and urine. Its presence 

 therefore has some diagnostic importance. 



A very interesting body which is sometimes found in the urine is 

 homogentisic acid. It is thought to be an intermediate step in the metab- 

 olism of tyrosme, and is found in the urine of people suffering from 

 alkaptonuria. The disease is remarkable in that it appears to run in 

 families and produces no ill effects. Homogentisic acid is a strong 

 reducing agent, and for this reason may be confused with sugar in 

 Fehling's test. 



The inorganic constituents of the urine include the acids: chlorides, 

 sulphates and phosphates; and the bases: sodium, potassium, magnesium, 

 and calcium. 



The Salts of the Normal Urine 



The Chlorides. The chlorides compose the bulk of the acid rad- 

 icles in the urine. Although they appear to be necessary constituents 

 of the living cell, they do not, so far as known, enter into combinations 

 with the organic constituents. The tissues appear to require a rather 

 definite concentration of sodium chloride in order to carry on their 

 work, for reduction in the sodium-chloride intake of the body results 

 in a reduction in the chloride excretion by the urine. In salt starvation 

 the chlorides may disappear entirely from the urine, the amount of 

 chloride excreted appearing to be closely related to the amount of salt 

 ingested. When the intake is constant, the rate of excretion is likewise 

 more or less constant, but a sudden reduction in the salt of the diet may 

 be accompanied by a slight decrease in the salt content of the blood, 

 with an attendant loss of water. On the other hand, when the salt is 



