204 INJURY, RECOVERY, AND DEATH 



accurately sketched with the camera lucida and kept 

 under continuous observation. In the course of ten min- 

 utes, 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 0.18 M CaCl 2 solu- 

 tion, 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 0.4 M NaCl, they were plasmolyzed and they 

 afterward expanded as before. 



Certain facts may be worthy of mention which tend 

 to obscure these results and which may have caused 

 them to be overlooked. 



In the experiment just described, the cells were trans- 

 ferred to a favorable solution as soon as expansion was 

 complete. If this precaution be neglected and the cells be 

 allowed to remain in the solution of NaCl, the injurious 

 action of the salt soon causes the protoplast to shrink. 

 In salts which are more toxic than NaCl, this contraction 

 may be more rapid and more pronounced. This shrink- 

 age, which may be called false plasmolysis, 8 may also be 

 produced by very weak (hypotonic) solutions and has 

 nothing to do with plasmolysis, but may simulate it in 

 very misleading fashion. If the cells are not continuously 

 observed, but only examined at intervals, the expansion 

 of the protoplast may easily be overlooked, and the sub- 

 sequent shrinkage may be easily mistaken for plasmolysis. 

 It is therefore desirable to keep the same individual 

 cell under observation during the entire course of 

 the experiment. 



s Cf. Osterhout (1908, 1913, C). 



