490 



SCIENCE 



[N. S. Vol. XL. No. 1031 



The fact that determinations of electrical 

 resistance afford an accurate measure of vital- 

 ity enables ns to attach the same sort of quan- 

 titative significance to normal vitality as we 

 attach to normal size or to normal weight. 

 For this purpose we may construct a variation 

 curve and determine the mode in the usual 

 way. 



There is no reason to suppose that the vital- 

 ity of an individual organism is constant any 

 more than its weight is. There is probably 

 some fluctuation which usually passes unper- 

 ceived unless a quantitative method of detect- 

 ing it exists. The writer finds that some 

 substances which are normally produced in the 

 organism alter its electrical resistance. Cer- 

 tain reagents may produce marked alteration 

 of resistance without permanent injury. Tor 

 example, tissue of Laminaria having a resist- 

 ance of 1,020 ohms was placed in NaCl .52 M, 

 which had the same conductivity as the sea 

 water; in the course of a few minutes the 

 resistance feU to 890 ohms, but on being re- 

 placed in sea water it rose in the course of a 

 few minutes to the normal amount, where it 

 remained. This was repeated on the same 

 piece of tissue for several days without any 

 sign of permanent injury.* 



It is therefore evident that considerable 

 fluctuations in vitality may occur without leav- 

 ing any permanent record. 



The determination of electrical resistance 

 makes possible a quantitative treatment of 

 injury. It is obvious that this is as impor- 

 tant as a quantitative treatment of vitality. 

 The degree of injury may be defined as the 

 amount^ by which the resistance falls below 

 the normal net resistance. Temporary injury 

 may be defined as that from which the organ- 



Bible and after recovery the material may be used 

 for expeiimental purposes. In tMs way individ- 

 uals of different species or unlike tissues of the 

 same individual may be compared with respect to 

 vitality. Prom a theoretical standpoint it may be 

 desirable to use in place of the resistance its re- 

 ciprocal, the conductance. 



* Science, N. S., 36, 350, 1912. 



B This is best expressed as percentage of the 

 normal net resistance; the net resistance is found 

 by subtracting the resistance of the apparatus. 



ism fully recovers, while permanent injury 

 may be defined as that which is not followed 

 by complete restoration of the normal resist- 

 ance. ° 



Prom a theoretical standpoint it may be 

 desirable to use in place of the resistance its 

 reciprocal, the conductance. 



We may now turn our attention to the sig- 

 nificance of this method of measuring vitality 

 and injury. Since the conductivity of the 

 tissue is a measure of the permeability of the 

 protoplasm to ions it is evident that in this 

 method the permeability of the protoplasm is 

 u^ed as an indicator of its vitality. This is 

 in accord with the results of long experience. 

 In doubtful cases it has been customary to 

 determine whether a cell was alive or dead by 

 its ability to contract in a plasmolyzing solu- 

 tion or to resist staining by certain dyes. The 

 diffusion of certain substances out of the 

 cell has long been recognized as a sign of 

 death. All of these are tests of permeability. 

 These criteria have been successfully employed 

 in cases where there was nothing in the ap- 

 pearance of the cell to indicate whether it was 

 alive or dead. 



The writer has found that the method of 

 plasmolysis may be utilized to distinguish not 

 only between living and dead cells, but also 

 between cells of normal vitality and those in 

 which vitality has been impaired by certain re- 

 agents. In these experiments the reagent was 

 not allowed to act long enough to produce 

 permanent injury. 



Lack of space renders it impossible to go 

 into the details of these investigations, but 

 attention may be called to experiments already 

 published which may be interpreted from this 

 point of view.^ These experiments show that 

 cells recover more quickly from plasmolysis 

 (and consequently have greater permeability) 

 in solutions in which their vitality is im- 

 paired. 



For example it was found that in sea water 

 suitably diluted a cell of Bpirogyra when 



8 The term injury as used by the writer in pre- 

 vious papers is synonymous with the term perma- 

 nent injury as here defined. 



7 Science, N. S., 34, 187, 1911. 



