August 11, 1911] 



SCIENCE 



U 



elusions drawn from the rate of expansion, as 

 stated above. 



But the most striking proof possible of the 

 penetration of the salt is afforded by the fol- 

 lowing simple experiment. By dividing a 

 Spirogyra filament into several portions it 

 was found that it was plasmolyzed in .2M 

 CaCl, and in .38M NaCl but neither in .195M 

 CaOL nor in .375M NaCl. On mixing 100 c.c. 

 .375M NaCl with 10 c.c. .195M CaCl, and 

 placing other portions of the same filament 

 in it, prompt and very marked plasmolysis oc- 

 curred. Here we arrive at the extraordinary 

 result that hy mixing together two solutions 

 neither of which is ahle to plasmolyze we pro- 

 duce a solution which plasmolyzes strongly. 

 The experiment is so simple and striking that 

 it is admirable for class-room demonstration. 



It may be noted that in this experiment we 

 add to a solution of NaCl a solution of CaCl, 

 which is of much lower osmotic pressure. It 

 is evident that although the addition of the 

 CaCl, lowers the osmotic pressure, it never- 

 theless increases the plasmolyzing power of 

 the solution considerably. Evidently it can 

 do this by preventing the ISTaCl from pene- 

 trating the protoplasm or the two salts may 

 mutually prevent each other from going in. 

 The behavior of the cell indicates that in most 

 cases the latter alternative is to be preferred. 

 This will be fully discussed in another paper. 



In the course of time the cells in the mix- 

 ture of NaCl and CaCL may expand, but this 

 occurs very much more slowly than in pure 

 NaCl. The appearance of the cell then shows 

 in the clearest manner that it is not NaOl 

 alone which has penetrated and caused the ex- 

 pansion, but rather NaCl and CaCl^ to- 

 gether. This is evident from the fact that 

 the eifects which are characteristic of pure 

 NaCl are entirely absent. But though they 

 eventually penetrate they do so slowly and the 

 effect of slow penetration is very different 

 from that produced by sudden penetration 

 and this may largely explain why they act as 

 antidotes to each other. 



It is evident that while the mechanism of 

 antagonistic action may depend largely on 

 the mutual action of the antagonistic salts in 



preventing each other from entering we must 

 take into account their effect on the proto- 

 plasm within the cell as well as their effect 

 on the plasma membrane. 



Marine algae give similar results. 



The chief conclusions are as follows: 



1. The usual method of determining os- 

 motic pressure by plasmolyzing in salts of 

 Na and K is very erroneous. Salts of Ca give 

 more nearly the true osmotic pressure. 



2. Since one substance may greatly affect 

 the penetration of another it is unsafe to use 

 the co mm on method of adding a toxic to a 

 non-toxic substance and judging the penetra- 

 tion of the former by the plasmolytic action 

 of the mixture. 



3. It is possible to state which salts pene- 

 trate and at what rate of speed, and also how 

 various salts affect the permeability of the 

 plasma membrane. 



4. From these data we have a definite clue 

 to the nature of the plasma membrane. Since 

 all the salts studied penetrate it seems certain 

 that the membrane can not be lipoid because 

 these salts are not soluble in lipoid. Its be- 

 havior toward balanced solutions (together 

 with other facts) indicates unmistakably that 

 the membrane is proteid in nature. 



5. Antagonistic salts such as NaCl and 

 CaCl, hinder or prevent each other from en- 

 tering. To such an extent is this true that by 

 choosing solutions of ISTaCl and of CaCl, 

 which are not quite strong enough to plasmo- 

 lyze we produce by mixing them together a 

 solution which plasmolyzes strongly. 



The fact that these salts hinder or prevent 

 each other from entering may explain why 

 they act as antidotes to each other. But since 

 they may eventually penetrate to some extent 

 we must attach importance to their effect on 

 the protoplasm within the cell as well as to 

 their effect on the plasma membrane. These 

 two effects may be very similar. 



W. J. V. OSTERHOUT 



INDIANAPOLIS MEETING OF THE AMER- 

 ICAN CHEMICAL SOCIETY 

 It has become almost monotonous to write that 

 a meeting of the American Chemical Society was 



