METHODS OF ANALYSIS. 39 



Intermediate between the peptones and the amido acids is a 

 class of substances, recently described by Fischer," called peptids, 

 which are divided into two classes, the dipeptids and the polypep- 

 tids. The importance of Fischer's work can not be overestimated, 

 as a beginning has thus been made in the important problem of deter- 

 mining the construction of the proteid molecule. 



Kreatin and Kreatixin. 

 application op kreatinin test to meat extracts. 



Kreatin and kreatinin are two amido bodies which characterize 

 meat and therefore they are natural and essential constituents of 

 meat preparations. The other meat bases are important constitu- 

 ents of an extract of beef, but occur in smaller amounts. 



As kreatin is the principal amido body found in meat, we expect 

 to find it, together with kreatinin, its dehydrated form, in still larger 

 quantities in meat extracts. In several cases in which the extract 

 acted suspiciously, no kreatin was found, and grave doubts exist as to 

 the source of such products. True meat extracts give high kreatin 

 and kreatinin results, as well as high figures for meat bases. The 

 estimation of the kreatin and kreatinin is, therefore, a very important 

 determination and of great value in determining artificial and imita- 

 tion meat and yeast products, and in establishing the source and 

 purity of an extract of meat. 



The determination of kreatin and kreatinin was carried out as fol- 

 lows : Use an aliquot of the filtrate from the insoluble and coagulable 

 proteid determination, the amount depending on the character of 

 the extract. 6 The aliquot must contain sufficient total kreatinin, 

 after dehydration of the kreatin to kreatinin, to give a reading not 

 far from 8° on the scale of the Dubosc colorimeter after applying the 

 colorimetric method as outlined by Folin c for the estimation of krea- 

 tinin in the urine. Heat this aliquot with 5 cc of half-normal hydro- 

 chloric acid for three and a half hours on a steam bath under a reflux 

 condenser. Neutralize the hydrochloric acid by the addition of 5 cc 

 of half-normal sodium hydroxid, then add 15 cc of a saturated 

 picric acid solution, and 5 cc of 10 per cent sodium hydroxid. 

 Shake the solution and allow it to stand for five minutes; make up 

 to 500 cc and compare the color with a half-normal solution of potas- 

 sium bichromate in the Dubosc colorimeter. The half -normal 

 bichromate solution when the scale is set at 8° corresponds to .10 mg 

 of kreatinin and from this figure the amount of kreatinin in the ali- 

 quot is readily calculated. 



« Untersuchungen iiber Aminosauren, Polypeptide unci Proteine (1899-1906), Berlin, 

 1906. 



b Aliquot should represent approximately 0.2 gram of a first class, solid beef 

 extract. 



e Zts. physiol. Chem., 1904, 41 :223. 



