54 CARNEGIE INSTITUTION OF WASHINGTON. 



would tend to take position in the peripheral layer and to assume a 

 greater density by lessening the liquid phase in the surface layer. 



4. The external layer of any colloidal mass or of any layer where two 

 masses meet has invariably a composition determined by the constitu- 

 tion of the impinging mass. The formation of the cellulose wall, which 

 is first seen as a free plate between two separating protoplasts, has a 

 structure resulting from such action. The plasma of the plant being 

 highly carbohydrate, the external layer is consequently largely anhy- 

 dride of this material. The layers added internally to the initial wall 

 must be of the same character. Furthermore, for similar reasons, the 

 external layer of the plasma, the semi-permeable membrane, would 

 also be high in carbohydrate. The inclosing and boundary layers of 

 nuclei and of all special bodies in the protoplasm would have a similar 

 dual origin. 



5. Highly proteinaceous plasmas would form external layers which, 

 in conformity with the above, would not be cellulose or so high in carbo- 

 hydrate. The chitinous skins of some animal organisms offer an 

 inviting subject for examination in this connection. 



6. In so far as these limiting layers offer resistance to the passage of 

 substances in solution equally in both directions, or as they allow the 

 free passage of water and resistance to substances in solution, they form 

 an osmotic machine by the action of which pressures may be set up 

 internal to the cell and to plasmatic or nuclear masses. The implied 

 phenomena designated as turgidity are most marked in plant cells, 

 where distentive forces of 40 or 50 atmospheres are found. It is to be 

 noted also that when the two elements of a plasmatic colloid, the carbo- 

 hydrate and the albumin, are unequally hydrated, as is the case in 

 nearly all solutions, the superior increase of one element in the complex 

 meshwork would set up something akin to osmotic pressure. 



7. Hydration increases, or swelling, are the result of the combination 

 of molecules of water with colloidal aggregates of the mass. The 

 addition of any substance which forms combinations with the colloidal 

 carbohydrate or protein may give systems v/hich attract, combine 

 with, and hold proportions of water different from those displayed when 

 water only is present. 



8. The hydration increase, or swelling of an intermeshed pentosan- 

 protein colloid, such as we imagine protoplasm to be, involves the 

 possibility of the unequal increase of these two main components under 

 the influence of any substance or ion, and the measurable alterations in 

 volume will be the resultant of the effects of such a substance or ion 

 upon the hydration of the unlike components. 



9. The pentosans are weak acids and in general their hj^dration 

 capacit}^ is lessened by hydrogen ions. Hydroxyl ions and compounds 

 containing the amino-groups, such as may be in solutions of phenyl- 

 alanin, alanin, asparagin, and glycocoll, may exert an effect by which 



