90 INJURY, RECOVERY, AND DEATH 



and similar in age, size and general characters, are placed 

 under the same unfavorable conditions, the one which lives 

 longest may be said to have the greatest vitality;" the 

 one which lives next longest may be rated second in this 

 respect, and so on. Determination of the electrical resist- 

 ance of these individuals enables us to predict at the 

 outset which will live longest, which next longest, and so 

 on through the entire group. 



It is therefore obvious that determinations of electri- 

 cal resistance afford a means of measuring vitality and 

 in the course of an extensive series of experiments it has 

 been found that this method may be relied upon to give 

 accurate results. 



The fact that determinations of electrical resistance 

 afford an accurate measure of vitality enables us to 

 attach the same sort of quantitative significance to nor- 

 mal 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 vitality of 

 an individual organism is constant any more than its 

 weight is. There is probably some fluctuation which 

 usually passes unperceived unless a quantitative method 

 of detecting it exists. 



The writer finds that all substances (whether organic 

 or inorganic) and all agents (such as excessive light, 

 heat, electric shock, mechanical shock, partial drying, 

 lack of oxygen, etc.) which alter conductivity of the 

 protoplasm shorten the life of the organism. This is 

 equally true whether the alteration consists in an increase 



" It might be expected that this individual would also excel in other 

 respects. A discussion of these is unnecessary from our present stand- 

 point: in 80 far as they can be quantitatively treated they form proper 

 material for a supplementary investigation. 



