338 HOW TO SEE WITH THE MICROSCOPE. 



isfiictory as to lead to the employment of the approxi- 

 mate tubes in his general practice ; and the degree of 

 accuracy afforded by the use of these tubes is quite equal 

 to the ordinary demands of the medical profession. 

 The principal source of error arises, as we believe, from 

 the fact that the coagulated albumen will at times pack 

 closer in the tube than at others. By using three or 

 four tubes in one and the same analysis, taking the 

 mean of the results, the approximate process will, in 

 most instances, be all that can be desired. Proceed as 

 follows : 



In a clean evaporating dish, or a Florence flask, coag- 

 ulate by heat three fluid ounces of the urine to be 

 tested; set aside until nearly cold; shake well; now 

 take three marais tubes, fill the first full, also the 

 second with the treated urine and coagulum; pour the 

 remainder into the third tube, rinsing the dish with a 

 little water, adding the wash to the several tubes. The 

 three tubes can be thus made to contain the entire 

 coagulum from the three ounces of urine ; set aside for 

 twenty-four hours, after which time read the several 

 tubes; add the readings together and divide by three, 

 and every two whole cubic centimetres will represent 

 one grain of albumen to the ounce of urine. 



In the daily routine it will often suffice to use but 

 one tube, in which case all that is necessary will be to 

 coagulate a single fluid ounce of the urine; when cool, 

 shake, and pour into the approximate tube, rinsing the 

 dish as before, adding the wash to the tube ; at the end 

 ot twenty-four hours read off the amount of coagulum ; 



