W. J. V. OSTERHOUT 281 



for example, it is very small and temporary, even in 0.278 m CaCU 

 (which has the conductivity of sea water). 



As was to be expected from experiments on other organisms^^ 

 La(N03)3 also produces a rise in resistance which is followed by a fall. 



One fundamental principle is evident in the results of all the ex- 

 periments, including those on plasmolysis and on electrical con- 

 ductivity; namely, that in solutions which are injurious the resistance 

 eventually falls, while in non-toxic solutions it remains practically 

 unaltered. This has been interpreted as indicating that injury is 

 accompanied by an increase of permeability, but the evidence for this 

 view was obtained by indirect methods and the writer welcomed the 

 opportunity to test it by the direct method of examining the cell sap. 



The experiments on sap were confined to the determination of 

 NO3, since it was found that the cells normally give tests for Na and 

 Ca. Since the method employed was not sensitive enough to detect 

 NO3 in the sap of the control cells under any circumstances, it is 

 evident that if a test was obtained after exposure to a solution con- 

 taining NO3 it must have been due to penetration from without. 



The sap was tested by placing it on a glass slide, adding a drop of 

 nitron dissolved in 10 per cent acetic acid, and observing it under the 

 microscope. If NO3 is present it may be recognized by the formation 

 of characteristic crystals. 



Cells kept for 24 hours in 100 cc. NaN03 0.05 m plus 10 cc. Ca(N03)2 

 0.05 M gave no test, which shows conclusively that the method is 

 safe as far as contamination by NO3 on the surface is concerned. 

 After 48 hours a test was obtained. As the cells continued to live 

 in this solution for 3 weeks (at which time the experiment was dis- 

 continued) and as they appeared normal in every way, it is evident 

 that the penetration was not the result of injury. 



It is probable that in 24 hours there was some penetration which 

 was not revealed by the test. This, however, has no significance in 

 the present investigation, the aim of which is not to determine the 

 absolute amount of penetration but merely to compare the relative 

 penetration in balanced and unbalanced solutions. 



The results of such a comparison are very striking. After 3 hours 

 in NaNOs 0.05 m a good test was obtained. The cells had lost some 



i^Osterhout, W. J.V., Bot.Gaz. 1915, nx,-i64; J. Gen. Physiol. 1918-19,1,299,409. 



