EXAMINATION OF NORMAL AND ABNORMAL URINE. 465 



Detection of albumin. Serum-albumin and serum-globulin are 

 the forms most frequently present in urine, but peptones and other 

 albuminoids are also met with. The different methods by which the 

 presence of albumin in urine is demonstrated are based upon the 

 coagulation of albumin. This coagulation may be accomplished by 

 heat, by nitric acid, by picric acid, by potassium ferrocyanide in the 

 presence of acetic acid, and also by either metaphosphoric or tri- 

 chloracetic acid. 



The urine used for any of these tests must be perfectly clear; if it 

 be not clear, it must be rendered so by processes which vary accord- 

 ing to the nature of the substance causing the turbidity. In most 

 cases filtration through good filter-paper may be sufficient ; but if this 

 does not accomplish the desired result, it may become necessary to 

 use other means. Thus, if earthy, amorphous phosphates be present 

 (which, especially in alkaline urine, are apt to pass through the best 

 filter-paper), they may be removed by adding to the urine about a 

 fourth part of potassium hydroxide solution, warming the mixture, 

 and filtering. If the turbidity be caused by urates, the urine will 

 generally become clear by passing the test-tube once or twice through 

 a flame. 



The clear urine is then tested by either (or all) of the following 

 methods : 



a. Coagulation by heat. A test-tube is filled about one-half with 

 the urine, to which, if not distinctly acid to test-paper, a few drops 

 of acetic acid are added. 1 (In case potassium hydroxide has been 

 added in order to precipitate the phosphates, enough of acetic acid 

 must be added to cause a distinct acid reaction.) The test-tube is then 

 held over the flame in such a manner that the heat acts upon the upper 

 half of the urine only, heating this portion gradually to near the boil- 

 ing point. By thus operating, two strata of fluid are obtained for 

 comparison, and by holding the test-tube against the light, or against 

 a black background, any difference in the appearance of the upper 

 and lower strata may be noticed. Any cloudiness or opacity seen 

 may be due to albumin, but may also be caused by earthy phosphates, 

 because these are often precipitated by heating, and have been mis- 

 taken for albumin quite frequently. 



The reason why phosphates are often precipitated by heating of urine is this : 

 Urine, showing a slightly acid or neutral reaction, contains dicalcium and di- 



1 If acetic acid alone causes a precipitate, this may be due to mucin, which should be filtered 

 Off before heating. 



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