270 PRACTICAL PHYSIOLOGY 



The tests employed, depend on certain of the reactions described under 

 proteids. It is obvious, of course, that the colour reactions will not be 

 applicable to the urine, those employed depending on the production of 

 coagula. The most important of these are : 



1. Heat Coagulation. EXPERIMENT I. Place some dear urine in 

 a test tube, and boil. A white turbidity or coagulum indicates that 

 either albumin or phosphates are present (earthy phosphates are pre- 

 cipitated by boiling). To the boiling solution, whether it show a 

 turbidity or not, add 3-4 drops of concentrated nitric acid. If due to 

 phosphates, the turbidity will disappear, but will remain if due to 

 proteid. In nitric acid any acid- or alkali-albumin which the urine 

 may contain is insoluble. Where there is doubt as to the occurrence 

 of a haze, the test tube should be about three-quarters filled, and only 

 the upper layer should be boiled, the test tube being meanwhile held 

 low down. By holding it against a dark background the slightest 

 haze becomes very evident by this method, on account of contrast with 

 the unboiled layer beneath. 



2. Heller's Test. EXPERIMENT II. Place some clear urine in a test 

 tube. Hold the test tube in a slanting position, and allow concentrated 

 pure nitric acid to run very slowly down the side, so that it forms a layer 

 underneath the urine. Where the two meet, a sharp white ring (of coag- 

 ulated acid albumin) is formed. The test may also be done by placing 

 the nitric acid first in the test tube, and covering this with the urine 

 slowly delivered from a pipette. The ring does not disappear on 

 warming. A similar ring may be obtained when proteoses are present, 

 but in this case the ring clears up on gently warming the test tube, and 

 reappears on cooling. In warming, very great care must be taken that 

 no mixing of the two layers occurs. When mucin is present in excess 

 a diffuse Jiaze may be produced in the portion of urine next the acid. 

 Also when the urine is very concentrated acid urates or urea nitrate 

 crystals may develop and simulate the reaction. In these cases, the 

 urine should be diluted with two or three times its bulk of water, and 

 the test reapplied, when very little doubt will remain as to the reaction. 



3. Salicyl-Sulphonic Acid Test. This is perhaps the most delicate of 

 all the tests. 



EXPERIMENT III. Add to about 10 c.c. of urine a drop or two of a 

 saturated solution of pure salicyl-sulphonic acid. A white precipitate 

 results, which on boiling changes into a number of coagula. 



This reaction occurs in a dilution of 1-230,000 albumin. The 

 only other body with which this reagent produces a precipitate 

 is proteose, in which case, however, the precipitate disappears on 

 warming. 



