146 E. E. FREE 



The hypothesis outhned seems preferable to the "sieve" 

 theory of Traube^^ and Ruhland^^ ^^^j to the "Hpoid" theories of 

 Overton^^ and Nathansohn^* for the reason that it explains the 

 frequent and normal changes of permeability for which those 

 theories fail to account. Comparison with the recent hypotheses 

 of Spaeth and of Clowes must be a little more detailed. Spaeth 

 ascribed alteration of permeability to a change in the viscosity 

 of the surface layer of the cell following a change in the "degree of 

 dispersion" of the protoplasmic colloids. There is an uncertainty 

 as to what is meant by "degree of dispersion." As commonly 

 used this term refers to a change in the size of the dispersed 

 particles of a colloid either by division of each of these particles 

 into smaller ones (greater dispersion) or by aggregation of several 

 particles into single larger ones (less dispersion). However, the 

 context implies that Spaeth refers to swelling or shrinkage of the 

 particles rather than to disintegration or aggregation of them. 

 If this is so the Spaeth hypothesis differs from the present one 

 only in that the mechanism by which swelling or shrinkage of the 

 globules is brought about, namely, water exchange between the 

 phases, is not suggested. Also, a regulation of permeability 

 by restriction of the paths of entry between the globules would 

 be much more effective and precise than any regulation which 

 might be produced by the mere change of viscosity which Spaeth 

 assumes. Such a change of viscosity would occur together with 

 the change in size of the globules but would have much less effect 

 on permeability. 



The chief objection to the hypothesis of Clowes is that the 

 phase inversion which it postulates would produce a change in 

 the permeability relations of the cell much more sudden and 

 complete than is actually observed. When phase inversion oc- 

 curred the cell would cease all at once to be permeable to the set 

 of substances soluble in one phase and become immediately 

 permeable to another set of substances, namely, those soluble 



" Arch. Anat. und Physiol. 1867: 87-165. 



12 Jahrb. wiss. Bot. 46: 1-54 (1909); Biochem. Zeits. 54: 59-77 (1915). 



13 Vierteljahrschr. naturf. Ges. Zurich 44:88-135 (1899); Jahrb. wiss. Bot. 

 34:669-791 (1899). 



" Jahrb. wiss. Bot. 39: 607-644 (1904) ; 40, 403-442 (1904). 



