METABOLISM 587 



from the paper, dissolve them in a very small amount of hot water and percolate 

 the hot solution through thoroughly washed animal charcoal, being careful to wash 

 out the last portion of the hippuric acid solution with hot water. Filter, concen- 

 trate the nitrate to a small volume and stand it aside for crystallization. Examine 

 the crystals under the microscope and compare them with those in Fig. 125, page 389. 

 This method is not as satisfactory as Roaf's method (see below). 



(6) Roaf's Method. Place the urine in a casserole or precipitating jar and add 

 an equal volume of a saturated solution of ammonium sulphate and 1.5 c.c. of 

 concentrated sulphuric acid per 100 c.c. of urine. Permit the mixture to stand for 

 twenty-four hours and remove the crystals of hippuric acid by filtration. Purify 

 the crystals by recrystallization according to the directions given above under First 

 Method. Examine the crystals under the microscope and compare them with those 

 given in Fig. 125, page 389. 



It is possible, by the above technic, to isolate hippuric acid in crystalline form 

 from as small a volume as 25-50 c.c. of herbivorous urine. The greater the amount 

 of ammonium sulphate added the more rapid the crystallization until at the satura- 

 tion point the crystals of hippuric acid sometimes form in about ten minutes. 



H. METABOLISM PROCEDURES INVOLVING THE 

 MANIPULATION OF THE FECES 1 



24. "Separation" of Feces. In order to differentiate the feces 

 which correspond to the food ingested during any given interval it is 

 customary to cause the person under observation to ingest some sub- 

 stance, .at the beginning and end of the period in question, which shall 

 sufficiently differ in color and consistency from the surrounding feces as 

 to render such differentiation comparatively easy. Two " markers" 

 very widely used in such tests are wood charcoal and carmine. In 

 making an actual separation of feces in a metabolism experiment 

 proceed as follows: Just preceding or in the early part of the first meal 

 (usually breakfast) of the metabolism test, ingest a gelatine capsule 

 (No. oo) containing 0.2-0.3 gram of carmine or charcoal. From this 

 time collect all stools in flat-bottom porcelain dishes and examine for the 

 presence of the " marker." All fecal matter containing portions of the 

 marker may be considered as representing the diet in question. This 

 fecal matter should be retained and preserved (see page 588). Just 

 before or in the early part of the first meal (usually breakfast) following 

 the end of the metabolism test a second "marker" in a gelatine capsule 

 should be ingested. The feces should be carefully inspected until the 

 marker makes its appearance. Retain all fecal matter uncolored by 

 the marker, reject the remainder. Frequent difficulties are encountered 

 in the practical separation of feces, but the character of such difficulties 

 will be most satisfactorily impressed by the performance of actual 

 separations. 



1 For other practical work on feces see Chapter XIV. 



