586 



Mr. W. Cramer. Surface Tension as a 



actions of these ferments in vitro under the usual conditions, and which have 

 therefore escaped observation. 



If one compares the conditions under which chemical processes proceed 

 in vivo with the experimental conditions under which the same processes are 

 usually studied in vitro, one finds as the most obvious difference that in the 

 latter case the influence of surface energy is reduced to a minimum, while in 

 the former it is developed to a maximum. In vivo there are interfaces 

 between cytoplasm and the surrounding medium, cytoplasm and nucleus, 

 cytoplasm and deposits in the cytoplasm, besides the interfaces presented by 

 the various colloids constituting the cytoplasm. In the conditions usually 

 obtaining in experiments in vitro all these sources of surface energy are non- 

 existent ; only the colloidal nature of ferment or substrate may give rise to 

 surface-tension effects, as they do, of course, also within the cell. 



The question is therefore whether surface-tension effects (apart from those 

 possibly caused by the colloidal nature of ferment or substrate) are factors 

 conditioning the action of ferments. It was found that when this factor of 

 surface tension was introduced by allowing the reaction to proceed in a test- 

 tube filled with glass beads or in a capillary glass tube, so that the surface 

 was increased, the action of invertase, diastase, and lipase was distinctly 

 retarded. 



A detailed account of the results observed with invertase is given in the 

 preceding paper. 



Further analysis of the phenomenon showed that the two phases which can 

 be distinguished in the action of a ferment are probably both subject to the 

 influence of surface tension, firstly the combination of substrate and ferment, 

 and secondly the chemical reaction which takes place in the substrate and in 

 which the ferment acts as a catalyst. 



While these observations establish the principle that ferment action is 

 conditioned by surface tension, they can only give a faint and incomplete idea 

 of the degree to which this factor controls the action of ferments within the 

 cell. For, compared with the immense development of surface which obtains 

 in the living cell and the living organism, the increase in surface energy pro- 

 duced by the presence of glass beads in the mixture of ferment and substrate 

 is very small. It must also be borne in mind that the experimental condi- 

 tions deal with surface tension between glass and a watery solution, while in 

 vivo surface-tension effects are produced between colloidal solutions of different 

 composition, membranes, colloids in the form of gels, and so forth. Lastly, 

 the effect of surface tension may vary with the nature of the ferment, of the 

 substrate and of the products of ferment action, according to the " surface 

 activity" of these substances, i.e. their property to lower surface tension. 



