CILIARY ACTIVITY 33 



ion concentration, to determine the penetration of cells by 

 acids and alkalis. Pantin has applied the same method of 

 attack to test whether there is an increase of hydrogen ion 

 concentration within the cell during pseudopodium formation. 

 The dye successfully employed for this purpose was neutral 

 red, which has its turning point in the neighbourhood of 

 absolute neutrality (becoming red on the acid side), is non- 

 toxic, readily absorbed by protoplasm, and has a negligible 

 protein error. The colorometric determination of proto- 

 plasmic pH. is facihtated by focussing an image of the standard 

 indicators on the observation slide by aid of the achromatic 

 condenser. 



By this method Pantin found that the hydrogen ion concen- 

 tration of the normal endoplasm and ectoplasm respectively 

 corresponded to a pH. of about 7*6 and 7*2 (in the resting 

 amceba the difference between ectoplasm and endoplasm 

 tended to be rather less than during active progression), but 

 the formation of a pseudopodium is preceded by a local 

 intensification of the red tint, indicating increased hydrogen 

 ion concentration ; while retraction of the pseudopodium is 

 accompanied by a local reduction of hydrogen ion 

 concentration. 



Such considerations have led the above-named author to 

 suggest an hypothesis of the mechanism of amoeboid action on 

 rather different lines from those advocated by previous workers. 

 These for the most part have sought to interpret pseudopodium 

 formation as the consequence of a local lowering of surface 

 tension in a system which is for the purpose regarded as a 

 fluid drop in an immiscible medium. There are in the surface 

 phenomena exhibited by simple fluid systems remarkable 

 analogies to the behaviour of the amoeba. BayHss quotes from 

 Rhumbler a picturesque phenomenon which occurs when 

 particles of glass fibre coated with shellac are brought into 

 contact with a globule of chloroform suspended in water. 

 The chloroform drop first envelops the particle, then, after 

 sufficient time has elapsed to permit of the shellac being 

 dissolved away, rejects the glass remainder, thus resembling 

 an amoeba swallowing a diatom and defaecating the insoluble 



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