

1920] SEI FRIZ— PROTOPLASM 365 



will set at a temperature of 21 C. This value as a minimum for 

 that temperature must certainly be erroneous. Bechhold speaks 

 of a 1 per cent dispersion of gelatine as a semifluid gel (presumably 

 at room temperature), and states that "aqueous" solutions (con- 

 taining only 1 per cent of water-free gelatine) gelatinize at "ice- 

 box temperature." I find that as low as an o. 8 per cent dispersion 

 (depending on the kind of gelatine used) will gelatinize, that is 

 form a soft jelly, at 18 C. In view of the fact that I have employed 

 a standardized gelatine, it is possible that the values of viscosity 

 given may be fairly accurately verified. I have deemed it advisable 

 to add another column of familiar substances, however, which will 

 help stabilize the scale, and which will also more clearly indicate 

 the exact consistency meant by any given value. 





and 



While a high consistency of an emulsion is almost conclusive 

 evidence of the gel state and a very low consistency evidence of 

 the sol state, yet viscosity alone is not a dependable criterion of 

 the sol and gel conditions. When the viscosity is of an intermediate 

 grade it is of no value as even an approximate indication of the 

 colloidal state. It will be well, therefore, to consider to what 

 extent we are justified in using the terms gel and sol as descriptive 

 of the physical state of protoplasm when viscosity is the only 

 criterion. Although we read that "gels are solid" (19, p. 230), 

 and although the word gel connotes to most of us a rather firm 

 though elastic body, it is not necessarily true that all gels are rigid. 

 In fact, this is not the case; a gel may be quite soft. Freundlich, 

 I believe, uses as an indication of the gel state the fact that the 

 substance will support a glass rod placed upright in it. Any 

 criterion of the gel state based on viscosity alone at best can be 

 only approximate. Physical structure and not viscosity deter- 

 mines the colloidal state. We have really no ready means of 

 determining in all instances the actual physical structure of pro- 

 toplasm, and probably, therefore, should do away with the expres- 

 sions sol and gel when the degree of viscosity is the only indicator 

 of one state or the other. Where the consistency is very high or 

 very low, however, we can safely characterize the living emulsion 



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