240 PROTOPLASM 



evidence are sufficient to recommend the emulsion hypothesis 

 of protoplasmic structure to many sound workers (page 288). 



There can be no doubt but that the protoplasmic emulsion 

 plays an important role. It presents a multitude of surfaces, 

 and it is at surfaces that reactions take place. But there are a 

 number of very charactejistic properties of protoplasm which 

 cannot be explained on the basis of emulsion structure. Proto- 

 plasm is elastic, and emulsions not (when pure). Protoplasm 

 coagulates, and emulsions do not. When milk coagulates, a 



protein (caseinogen) coagulates and not the 

 emulsion of butterfat. Emulsions exhibit 

 phase reversal, and on this property does the 

 emulsion theory of protoplasmic behavior rest, 

 yet there is no evidence whatever of phase 

 reversal in protoplasm. It is very improbable 

 indeed that the dispersion medium of pro- 

 toplasm could become the dispersed phase 

 (pages 288-289). Electrical conductivity 

 measurements by Gelfan reveal that the 

 conductivity of protoplasm is the same at all 

 Fig. 1 1 7. Red viscosity values. Blood also shows no change 

 blood cells of A, [y^ conductivity in spite of a great increase 



Triton, B, Crypto- . ■ ■. / m. c i i- n 



branchus, with nuclei, m viscosity (as a result of coagulation), 

 showing alveolar Arrhenius found this to be true of gelatin 



structure. {A, from ^ .. , r i j_- j. i j 



J. Comandon.) when it sets Irom a solution to a gel, and on 



this basis McBain denied the possibility of 

 phase reversal when soap jellies are formed. The whole idea 

 of phase reversal has been discarded as a property of gel-forming 

 systems. 



We may now consider some of the special forms that the visible 

 protoplasmic emulsion assumes. 



The Alveolar Hypothesis. — The German protozoologist 

 Blitschli observed a very symmetrical honeycomb or checker- 

 board appearance in the protoplasm of certain organisms. He 

 regarded this structure as fundamental. It seemed to be made 

 up of tightly compressed globules which, owing to pressure, 

 become angular, their geometrical shape being that of dodeca- or 

 tetrakaidecahedrons. In optical cross section, the globules 

 present a hexagonal outline. Biitschli called them alveoli. The 

 structure is plainly visible in certain Protozoa, such as Euplotes 



