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W. J. V. OSTERHOUT 



solution. Within two minutes the protoplasts of most of the 

 cells were so far plasmolyzed that they no longer touched the 

 end walls of the cells. Several of these were accurately sketched 

 with the camera lucida and kept under continuous observation. 

 In the course of ten minutes several of them had begun to expand 

 and in thirty minutes all had expanded so as to completely fill 

 their respective cells. To avoid the injurious action of the salt, 

 the filaments were then transferred to 0.18M CaCL solution and 

 this was gradually diluted until its osmotic pressure was not 

 greater than that of tap water. The cells were then transferred 

 to tap water. They were examined the next day and found to 

 be alive. On being placed in 0.4M NaCl they were plasmolyzed 

 and afterward expanded as before. 



Recovery from plasmolysis is about as rapid in KCl as in NaCl, 

 while in CaCU it is much slower.^ 



The most striking proof of the penetration of the salt is afforded 

 by the following simple experiment. By dividing a Spirogyra 

 filament into several portions if was found that it was plasmolyzed 

 in 0.2M CaClz and in 0.38M NaCl but neither in 0.195M CaCU 

 nor in 0.375M NaCl. On mixing 100 cc. 0.375M NaCl with 10 

 cc. 0.195M CaCU and placing other portions of the same filament 

 in it, prompt and very marked plasmolysis occurred. By mix- 

 ing together two solutions neither of which is able to plasrnolyze we 

 produce a solution which plasmolyzes strongly. The experiment 

 is so simple and striking that it is admirable for class-room dem- 

 onstration. 



It may be noted that in this experiment we add to a solution 

 of NaCl a solution of CaCU which is of much lower osmotic 



^ It should be pointed out that it is very easy to overlook recovery in salt 

 solutions if the precautions described above are not carefully observed. Unless 

 the same individual cell is kept under practically continuous observation during 

 the first period of the experiment, recovery may occur and be succeeded by false 

 plasmolysis in an interval between observations. If the false is mistaken for 

 the true plasmolysis (as frequentlj' happens) the observer will be fully convinced 

 that no recovery has taken place. With some species there is no recovery for the 

 reason that false plasmolysis occurs too quickly to permit it. And the use of a 

 standard balanced solution and of uniform material is necessary where we wish 

 to compare the speed of recovery in different salts. 



