70 THE GENERAL CHARACTERS OF THE PROTEINS 



The reaction with dilute formaldehyde solutions (e.g., 4 c.c. of a 

 2 per cent, solution added to 10 c.c. of a protein solution) was 

 somewhat slow ; the maximum amount of aldehyde had not, as a 

 rule, entered into reaction until after two to three weeks ; after this 

 interval it was found that I gram of gelatin (a 10 per cent, solution 

 of which had been boiled to prevent subsequent setting to a jelly) 

 combined with 0*0135 gram formalin ; 10 c.c. fresh egg-white 

 combined with 0*375 g ram > 2 grams powdered egg-white with 

 0*0360 gram, 10 c.c. blood-serum with 0*315 gram, 3 grams fibrin 

 with 0*0345 gram, and 5 grams caseinogen with 0*0294 gram for- 

 maldehyde. The compounds thus formed were no longer digestible 

 when treated with pepsin, but could be decomposed when distilled 

 with steam, and a digestible protein could be thereby recovered ; the 

 formaldehyde could also be quantitatively recovered in the distillate. 

 Similar results to those of Benedicenti have been obtained recently 

 by Treves and Salomone. 



Schiff has also investigated the action of formaldehyde on 

 proteins. He added a concentrated solution of formaldehyde (40 

 per cent.) to a solution of proteins, and then estimated the acidity of 

 the latter. The reaction which takes place is assumed to be similar 

 to that which takes place with the amino-acids. The amino group 

 entering into reaction with the aldehyde forms methylene derivatives ; 

 the alkalinity due to the presence of such groups is thereby elim- 

 inated, and the acid, which before treatment acts practically as a 

 neutral body to most indicators, now becomes strongly acidic in 

 character, and can be titrated directly with alkalis, with the use of 

 phenol-phthalein. By using this method Schiff found that I gram 

 molecular equivalent of potassium hydroxide neutralised 3,231 grams 

 of egg-albumin and 4,680 grams of gelatin, after solutions of the 

 latter had been treated with formaldehyde. The titrations were 

 carried out in some cases directly after mixture of the proteins with 

 the aldehyde, and in other cases after the mixtures had stood for 

 twenty-four or forty-eight hours. The same amount of alkali was 

 required for neutralisation in each case. The result is not quite in 

 accord with those of Benedicenti, who found the reaction was only 

 complete after two or three weeks ; he used, however, only very weak 

 aldehyde solutions, whereas Schiff used the undiluted commercial 

 preparation (40 per cent). 



The results seem to indicate that the reaction may be of use in 

 estimating: the amino and carboxyl groups in individual proteins, and 

 thereby obtaining other factors for their characterisation. It has 

 been already employed by Sorensen in studying the process of 

 digestion of proteins by enzymes. As hydrolysis proceeds and the 

 polypeptide groups are broken down, the number of free amino and 

 carboxyl groups in a given amount of the solution increases ; by treat- 

 ing the products of digestion with formaldehyde at different intervals, 

 and then titrating the mixture with barium or sodium hydroxide, 

 using phenol- or thymol-phthalein as indicator, Sorensen has succeeded 

 in obtaining a new factor for the study of proteolysis by enzymes. 



It seems possible that the amino and carboxyl factors in any 

 protein may be determinable by a similar method, if the suitable 

 experimental conditions be ascertained. Such factors might be of 

 value for their characterisation. 



