INJURY AND RECOVERY 91 



of conductivity, or in a decrease of conductivity (followed 

 by an increase), as is the case when certain reagents 

 (such as CaCl 2 ) are applied. This is a very striking 

 fact and its significance in the present connection seems 

 to be perfectly clear. It shows in a convincing manner, 

 that electrical resistance is a delicate and accurate 

 indicator of normal vitality. 



Since it is evident that a fall of resistance indicates 

 injury, it seems reasonable to assume that the amount 

 of fall is a measure of the amount of injury. This may 

 be expressed as per cent, of the total possible loss (this 

 would correspond to the amount of loss of the substance, 

 M, as previously discussed). If tissue which has been in- 

 jured by exposure to a toxic solution be replaced in sea 

 water, it may recover a part or all of the resistance which 

 it had lost. If the resistance should fall to 70%, then 

 recover in sea water to 90%, and remain stationary, we 

 might call the temporary loss of resistance temporary 

 injury and the permanent loss permanent injury. In this 

 case the temporary injury 16 would be 30-^90=33.33% and 

 the permanent injury 10-^90=11.11%. If we calculate the 

 protoplasmic resistance in this case we find that starting 

 at 100% the resistance decreases to 62.50% and recovers 

 to 86.4%. In the case of protoplasmic resistance the total 

 possible loss 17 is 92.65, the temporary injury is there- 

 fore (100 62.5) -~ 92.65 = 40.5% and the permanent 

 injury is (100 86.4) -^ 92.65 = 14.68%. In this manner 

 we arrive at a quantitative basis for the study of injury 

 and recovery. 



16 



We divide by 90 because if the resistance starts at 100 the total 

 possible loss is 90. This is merely another way of saying that we 



subtract 10 from 100 because the base line is taken as 10 (see p. 56). 

 17 I.e., the base line is 7.3-5%. 



