Lecture 3 — 69 — Absorption 



cells. HoBER (1940) has reported evidence of secre- 

 tory activity for certain kinds of dyes by kidney and 

 liver cells. Several theories of sugar transport in 

 animal or plant tissues invoke metabolic energy in 

 one form or another. 



Many attempts have been made to construct arti- 

 ficial cells to imitate, at least in some respects, the 

 action of living cells in their absorption or accumula- 

 tion of inorganic solutes. The general observation 

 might first be offered that even if in an artificial 

 system some function similar to that of the living 

 cell is performed, there is no necessary conclusion 

 that the cell achieves the same step in the same way. 

 Actually it does not appear that any artificial cell so 

 far proposed can accumulate salt in the same way as 

 does the living cell. 



One ingenious artificial cell has been devised in 

 which a layer of guaicol or similar substance repre- 

 sents the protoplasm, and by maintaining a hydrogen 

 ion gradient between inner and outer compartments 

 of the cell — that is, the pH is higher outside than in- 

 side — potassium accumulates (Osterhout, 1936). 

 The theory is that KOH reacts with the guaicol or 

 other substance and is released to the more acid solu- 

 tion inside. Undissociated molecules rather than ions 

 are considered to be primarily concerned in the initial 

 process of salt entry. The accumulation of anions is 

 not, however, directly accomplished, and many results 

 on living cells, including some reported on Nitella, and 

 extensive studies on roots in our laboratory, do not 

 appear to be consistent with the view that a pH gra- 

 dient of the kind suggested is indispensable to the 

 accumulation of potassium by plant cells. 



I do not wish to argue that important facts may 

 not be learned by the study of artificial cells or mem- 

 branes. We may expect that modern research on 

 oriented mono- and polymolecular films will have the 

 most valuable consequences for biology. What I do 

 wish to stress is that the solute movements in living 



