282 DETERMINATIONS OF PERMEABILITY 



of their turgidity; if left in the solution of NaNOs or if transferred to 

 tap water they subsequently lost all their turgidity, indicating death. 

 It is therefore evident that this rapid penetration was accompanied 

 by injury. 



It may be remarked that the turgidity of the cells is a good indica- 

 tion of their condition. It is easily tested by lifting them out of the 

 solution; if in good condition they appear stiff, if injured they tend to 

 collapse. It is, however, necessary to distinguish between loss of 

 turgidity in isotonic or hypotonic solutions, which indicates injury, 

 and a similar appearance in hypertonic solutions, which may indicate 

 nothing of the sort. In the latter case the ceU promptly recovers its 

 turgidity when placed in tap water; in the former it does not. 



Another criterion of injury is afforded by the appearance of the 

 chlorophyll bodies. In the normal cell they are arranged in regular 

 rows and are of a clear, transparent green color. When injury occurs 

 they lose their regular arrangement and their color becomes more 

 opaque. 



In 0.05 M Ca(N03)2 the cells live for a week or more. During the 

 first few days, at least, penetration is not more rapid (perhaps is less 

 so) than in a balanced solution. 



Similar results were obtained with other salts, which will be 

 described in a subsequent paper. 



The outcome of these direct tests is therefore a confirmation of 

 the results obtained by the indirect methods. We find that penetra- 

 tion in injurious solutions is relatively rapid as compared with 

 penetration in non-toxic solutions. This corresponds to the fact 

 that recovery from plasmolysis is more rapid in injurious solutions 

 as well as to the fact that conductivity increases in such solutions. 



In view of this we may conclude that determinations of electrical 

 conductivity give reliable information regarding changes in per- 

 meability. Observations on recovery from plasmolysis, while giving 

 similar results, are less satisfactory. 



SUMMARY. 



1. Methods are described for obtaining cell sap from Nitella with- 

 out contamination. 



