158 SENESCENCE AND REJUVENESCENCE 



lot of ten worms, i.e., this column gives the extremes of the survival 

 times and the fourth column the means. The table shows at a 

 glance that tjie susceptibility of the animals increases very greatly 

 during the course of starvation, the mean survival time decreasing 

 from seven Jiours and forty-five minutes in the large, well-fed 

 animals at the beginning of the starvation period to two hours in 

 the reduced ^nimals after ninety-one days of starvation. 



The changes in susceptibility have been determined in the same 

 way for several other starvation stocks, some made up from larger 

 animals than these, others from smaller, and still others from ani- 

 mals of the game size. Different stocks were kept during starva- 

 tion under various conditions of temperature, light, aeration, and 

 change of water, but in all essentially the same result was obtained, 

 viz., a great and, except for slight irregularities in a few cases which 

 were evidently due to incidental uncontrolled factors, a continuous 

 increase in susceptibiUty during starvation. 



According to the second method of procedure mentioned above, 

 the susceptibility of the starved animals may be compared directly 

 with that of fed animals. The records of two tests of this sort 

 are presented. 



In the first of these several hundred worms fifteen to eighteen 

 millimeters long were selected from freshly collected material as a 

 starvation stock. After eighty-one days of starvation the animals 

 were reduced to a length of seven to eight millimeters, and the 

 susceptibility of ten of the reduced worms is shown in the curve cd 

 of Fig. 56. For comparison the susceptibility curves of ten ani- 

 mals of the same size and condition as the members of the starva- 

 tion stock before reduction (e/. Fig. 56) and of ten well-fed, young 

 animals of the same size as the animals reduced by starvation {ah, 

 Fig. 56) are given. The young, fed animals are most, the old, 

 fed animals the least, susceptible, but the susceptibility of the 

 animals reduced by starvation is much nearer that of the young 

 animals than that of the old and therefore must have undergone 

 marked increase during reduction. 



In another case the starvation stock was composed of animals 

 twenty to twenty-four millimeters long, and the determination of 

 susceptibilities recorded in Fig. 57 was made after ninety days of 



