CRITICISM OF BERT 1 1 OLD 295 



of Amoeba', and to class the latter as adhering 'Imps of this 

 kind, as Uerthold does. His hypothesis start-, as has bem 

 said, from the view that the Aimeba adheres to th<- solid 

 substratum of the underlying surface and, being a fluid drop, 

 is subject to the above-mentioned conditions, in accordance 

 with which its marginal angle must also remain constant 

 as long as the chemical composition of the protoplasm is 

 constant. 



Now if, at a point of the edge of the Anneba, a chemical 

 alteration takes place, whereby a lowering of the surface 

 tension (a 12 ) between the protoplasm and the underlying 

 surface is brought about, or, as Berthold usually expresses 

 it, the adhesion between the substance of the Amceba and 

 the substratum is increased, there then results an extension 

 of this margin, until the marginal angle is sufficiently 

 diminished, to compensate for this change of the surface 

 tension or of the adhesion. If we have already reason 

 to doubt this explanation, on account of Quincke's ex- 

 perience to the effect that surface tension has no 

 influence upon adhering water drops, there are in 

 addition a considerable number of further points which, in 

 my opinion, are evidence against it. In the first place, 

 I consider it incorrect to suppose that Amoeba} really 

 adhere to the solid substratum. I do not entirely dispute 

 the fact that local adhesions at the hinder end, or occasion- 

 ally also in the pseudopodia during their retraction, may 

 come under observation. On the other hand, I consider 

 it certain that an extensive adhesion is absent. Any one 

 who has been frequently occupied with Amoeba? knows that 

 even very feeble currents of water are usually sufficient to 

 wash them away from the surface on which they are creep- 

 ing, while really powerful forces would in any case be 

 necessary for this, if an actual adhesion existed. In 

 addition to this there is the fact that some Amoebae, which 

 certainly do not adhere, but swim freely in the water, 

 develop pseudopodia, and their power of changing their 

 shape is in no way impaired. 1 



1 A very suitable object upon which to convince oneself of the non- 

 adherence of very motile Aino-biu is Fclon^is". With some good motile 



