444 BANANA GEL 



The formation of the gels by the direct addition of certain salts 

 under suitable conditions as well as by dialysis against solutions of 

 such salts is significant. It raises the question whether it would not 

 be possible in many cases to bring about reactions such as precipita- 

 tion, solution, etc., by direct chemical actions involving the addition 

 of reagents under definite conditions, in place of dialysis against solu- 

 tions of more or less accidental salt contents. The fact that such 

 solutions as the tap water which was used in the present investigation 

 may contain dissolved substances in minute concentrations only serves 

 to obscure the possible actions. These small concentrations of dis- 

 solved substances which may react, but which are constantly renewed 

 as the dialyzing liquid changes, are capable of producing effects which 

 larger initial concentrations would produce in shorter times. Thus, 

 the banana gel-forming substance inside the bags was able to react 

 with the calcium salts from the outside liquid and over the extended 

 period of time which was used here and is also used in most dialysis 

 studies, the reaction occurred, first along the inner walls of the bags 

 and finally throughout the liquid. The different hydrogen ion con- 

 centrations inside and outside the bags also served to confuse the 

 exact conditions at which the reactions could take place. 



These relations make it advisable in every case in which dialysis is 

 used to study the composition of the dialyzing liquid, as small amounts 

 of dissolved substances and also apparently unimportant differences 

 in hydrogen ion concentrations may result in the occurrence of 

 definite chemical changes. Also, the material of which the dialyzing 

 bags are made may exert profound effects upon the changes.^ The 

 plea may be made, therefore, to replace dialysis wherever possible by 

 direct additions of chemical reagents at the same time controlling 

 the hydrogen ion concentrations of the mixtures, and in this way sub- 

 stituting more or less accidental and to some extent unknown methods 

 of treatment by known and definite additions of chemical reagents. 



The results obtained therefore point to chemical reactions and com- 

 binations involving specific elements under definite and limited condi- 

 tions. Although it was not found possible to obtain these compounds 

 in pure condition as chemical individuals, the results can best be 

 interpreted on the basis of the formation of such chemical compounds. 



^ Brown, W., Biochem. J., 1915, ix, 591; 1917, xi, 40. Eggerth, A. H., /. 

 Biol. Chem., 1921, xlviii, 203. 



