OCTOBEE 2, 1914] 



SCIENCE 



489 



electrical measurements showed it to be dead.) 

 On tlie other hand, material of doubtful ap- 

 pearance often turned out to be much better 

 than that which looked to be in sound condi- 

 tion. It seems quite possible that this will be 

 found to be the case with other organisms when 

 quantitative tests are applied. 



Material collected in a restricted locality 

 and examined as soon as taken from the ocean 

 gave a very uniform resistance. The same 

 number of disks were used in each experi- 

 ment, and as the disks were packed together like 

 a roll of coins the length of the roll gave an 

 accurate measure of the average thickness of 

 the disks. To make the comparison as accu- 

 rate as possible disks of the same average thick- 

 ness were used in all the experiments. Under 

 these circumstances the resistance at 18° C. 

 did not vary much from 1,300 ohms. For ex- 

 ample, in a series of determinations of ten 

 different lots of tissue the highest reading 

 was 1,320 ohms and the lowest 1,285 ohms. 

 These lots of tissue were allowed to remain 

 in the laboratory under different conditions. 

 Some were placed in running salt water while 

 others were allowed to stand in still salt water 

 in pans of various sizes. Some of these were 

 placed in direct sunlight (where the tempera- 

 ture rose to an injurious point) while others 

 were kept in a cool place and sheltered from 

 direct sunlight. At the end of twenty-four 

 hours there was no difference in the appear- 

 ance of these lots, but their electrical resistance 

 varied from 400 ohms to 1,320 ohms. All were 

 then placed side by side in the same dish. 

 Those with the lowest resistance were the first 

 to die, as was shown by the fact that their 

 resistance feU to the death point (about 330 

 ohms) and became stationary. The others died 

 in the order indicated by their electrical re- 

 sistance. 



Determinations of the resistance made it 

 evident that in no case did visible signs of 

 death make their appearance until twenty-four 

 hours after death occurred, and subsequent 

 experiments showed that in some cases (espe- 

 cially at low temperatures and in the presence 

 of certain reagents) they may not appear until 

 several days after death. 



It was found that material from one local- 

 ity showed a low resistance and subsequent 

 examination showed that it was contaminated 

 by fresh-water sewage. The appearance of 

 the plants was not such as to lead to their re- 

 jection for experimental purposes. They did 

 not survive as long in the laboratory as plants 

 of normal resistance "taken from the other 

 localities. 



It may be taken for granted that vitality, 

 whatever else it may signify, means ability to 

 resist unfavorable influences. When organisms 

 which are of the same kind, 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 resistance of 

 these individuals enables us to predict at the 

 outset which will live longest, which next 

 longest, and so on through the entire group. 



Moreover, we find that all influences which 

 impair vitality lower the electrical resistance. 

 It is therefore obvious that determinations of 

 electrical resistance afford a means of meas- 

 uring vitality and in the course of an exten- 

 sive series of experiments it has been found 

 that this method may be relied upon to give 

 accurate results.^ 



2 It might be expected that this individual would 

 also excel in other respects. A discussion of these 

 is unnecessary from our present standpoint: in so 

 far as they can be quantitatively treated they 

 form proper material for a supplementary in- 

 vestigation. 



3 It is evident that the most accurate compari- 

 sons will be secured when the tissues or organisms 

 are closely similar in structure, for variations in 

 structure may cause variations in electrical re- 

 sistance. To compare tissues or organisms which 

 differ in structure (or which for any other reason 

 differ in the absolute number of ohms which ex- 

 presses their normal resistance) we may use the 

 fall of electrical resistance in a given time 

 under unfavorable conditions (expressed as per- 

 centage of the normal net resistance, as suggested 

 below in the discussion of injury) or we may use 

 the speed of recovery from injury of a definite de- 

 gree. The fall of resistance need not proceed be- 

 yond the point at which complete recovery is pos- 



