QUINCKE'S HYPOTHESIS 305 



remarks to a few words upon this, in my opinion, quite 

 untenable hypothesis. The forces which Berthold draws 

 upon to explain the development of the fine pseudopodia, 

 are of a chemical nature, namely, those which are sup- 

 posed to come into play during the solution of a solid 

 body, as exerting attractions between its molecules and those 

 of the solvent medium. Forces of this kind are supposed 

 to exert their activity between the surrounding medium and 

 the particles of the protoplasmic body, and, upon the supposi- 

 tion that its surface tension is very low, to be sufficient to 

 spin it out into fine pseudopodia. As can easily be seen, 

 this hypothesis recalls to some extent that of Mensbrugghe 

 described earlier (p. 65) with respect to the cause of the 

 pseudopodium-like outgrowths of oil-drops. I think, how- 

 ever, that Berthold's hypothesis is built upon much too 

 uncertain a basis, i.e. takes forces into account which are 

 altogether too hypothetical and uncontrollable for us to take 

 them earnestly into consideration. If Berthold's interpreta- 

 tion were correct, one might well expect that pseudopodium- 

 like processes would be seen to radiate out from a thick, 

 coloured gum solution, upon which water was poured, 

 which is by no means the case. 



In any case, however, it would seem in the highest 

 degree improbable that protoplasmic movements should 

 have four different causes ; it may rather be postulated 

 with some certainty that a common cause must lie at the 

 root of them all, even if it is not yet possible at the present 

 time to refer all the modifications to this cause. 



In 1888 Quincke developed, in connection with his 

 observations upon superficial extension-currents as the result 

 of local diminution of surface tension, certain views upon 

 the explanation of the protoplasmic streams in plant cells, 

 etc., which agree in the main with the first hypothesis given 

 by Berthold. In its details, however, Quincke's explana- 

 tion seems to me untenable, since he has not sufficiently 

 taken into consideration the state of things that actually 

 exists in the vegetable cell. Quincke has the following 

 idea of the structure of a plant cell. The protoplasmic 

 lining which occurs under the cell membrane consists of 



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