88 INJURY, EECOVEEY, AND DEATH 



ance/3 but if plants have been subjected to unfavorable 

 conditions^' their resistance is below the normal. This is 

 of considerable practical value, enabling the experimenter 

 to reject abnormal material, and is also theoretically 

 important, for it provides us with a measure of what 

 we may call the normal condition, or normal vitality, of 

 the organism. 



Although the idea of normal condition (or normal 

 vitality) is one of the fun.damental conceptions of 

 biology, it has never been precisely formulated : nor does 

 it seem possible to attempt this without the employment 

 of quantitative methods. The writer 's studies in this field 

 have led to a quantitative treatment of injury and recov- 

 ery, which may now be discussed. 



In practice, we determine the condition of material 

 by measuring the resistance of pieces of tissue or of 

 intact organisms. These investigations show that it is 

 often difficult to judge of the condition of an organism by 

 its appearance. Tissues were found to be capable of 

 losing much of their vitality without betraying it by 

 their appearance. (This was particularly the case with 

 the eel grass, Zostera, which retained its normal 

 green color and appearance for some days after 

 electrical measurements showed it to be dead). On the 

 other hand, material of doubtful appearance often 

 turned out to be much better than that which looked to be 

 in sound condition. 



Material collected in the same locality and examined 

 as soon as taken from the ocean gave a very uniform 

 resistance. To make the comparison as accurate as possi- 

 ble disks of the same average thickness were used in the 



"I.e., when the fronds are of about the same thickness, etc. 

 "C/. Osterhout, (1914, D). 



