METABOLISM AND THE DISTRIBUTION OF MATERIAL 241 



observe that by this chemical attack the layer which had been per- 

 meable for hydrophile substance became impermeable for them and 

 was made permeable for substances soluble in fat. However, we know 

 from the investigations of J. LOEB and W. J. V. OSTERHOUT (see p. 

 378, et seq.) that small amounts of divalent cations detoxicate neutral 

 salts by inhibiting, according to the view of J. LOEB, the free ex- 

 change of ions through the plasma pellicle. CLOWES extended his 

 observations to other polyvalent cations and the quantitative rela- 

 tions are in excellent agreement. 



The other tendency is to assume a pure albuminous membrane; 

 W. J. V. OSTERHOUT assumes this, as the result of the following 

 remarkable observation: he placed spyrogyra cells in common salt 

 solution of such concentration that no plasmolysis 1 occurred; when 

 he added very dilute calcium chlorid solution so as to depress the 

 osmotic pressure, plasmolysis occurred. The plasma pellicle must 

 have been permeable for NaCl and its passage is only impeded by 

 the CaCl 2 . In contrast to OVERTON'S view, OSTERHOUT regards the 

 plasma pellicle as permeable for most ions of the light metals and 

 consequently it must be albuminous. 



The action of the Ca-ion possibly depends on its antagonistic 

 action (see p. 69) though it may be due to a variety of tannage of 

 the plasma pellicle. With the death of the cell, the pellicle becomes 

 generally permeable. 



RUHLAND also, discards the lipoid theory. He considers only the 

 thickness of the. membrane to be responsible for permeability or 

 impermeability; the membrane acts like an ultrafilter in the sense of 

 BECHHOLD. He studied a large number of dyes, enzymes, alkaloids 

 and other substances which occur in plants and found that their 

 ability to penetrate the plasma cells was in proportion to their ability 

 to spread out in thick jellies; in other words, it depended on their 

 particle size (see p. 56). 



In view of the known facts we must admit that at present we can 

 arrive at no conclusion concerning the nature and structure of the 

 plasma pellicle. Of one thing we can be certain, that OVERTON'S 

 original theory of a continuous lipoid membrane must be abandoned. 

 I am of the opinion, however, that it is possible to conciliate the 

 theories which have been elucidated here and which seem to be 

 mutually exclusive. 



In the first place, the assumption of a pellicle of emulsified fat does 



1 Osterhout distinguished between true and false plasmolysis. The latter 

 may occur in dilute solutions even in pure water most usually in marine plants. 

 It is probably due to the coagulation of the protoplasm from the penetration of 

 the water. 



