114 SENESCENCE AND REJUVENESCENCE 



It is evident, then, from all points of view, that these different 

 forms represent different degrees of reconstitution. If the degree 

 of rejuvenescence, as indicated by the increase in susceptibility, 

 is associated with the degree of reconstitution, then these different 

 forms, when produced under comparable conditions, should show 

 the highest susceptibility in the normal, the lowest in the headless 

 animals, with intermediate conditions in the intermediate forms. 

 The following experiment shows to what extent this is the case. 



The stock for the experiment consisted of a hundred or more 

 pieces like a in Fig. 24, cut from animals of equal size and similar 

 physiological condition and allowed to undergo reconstitution 

 under uniform external conditions. Even under such conditions 

 pieces of this size and from this region may produce anything from 

 normal to headless forms, although the great majority are headless 

 or anophthalmic. 



Eleven days after section reconstitution was practically com- 

 plete, and the susceptibilities of lots of ten each of the different 

 forms and at the same time of a lot of ten intact worms like those 

 from which the pieces had been taken were determined. The 

 control animals had been kept under the same conditions as the 

 pieces, and, like them, without food during the eleven days of the 

 experiment, and the difference in susceptibility between the pieces 

 and these whole animals should show how much rejuvenescence 

 had occurred in connection with reconstitution. 



The results appear in the susceptibility curves of Fig. 25. The 

 curve of the whole animal is drawn in an unbroken line, that of the 

 normal animals developed from pieces in short dashes, that of 

 the teratophthalmic forms in long dashes, that of the anoph- 

 thalmic forms in alternate long and short dashes, and that of head- 

 less forms in dots. The susceptibility is highest in the normal 

 animals developed from pieces, slightly lower in the teratophthalmic 

 forms, considerably lower in the anophthalmic forms, and again 

 still lower in the headless forms. In all except the headless forms 

 the susceptibility is higher than in the whole animals, i.e., it has 

 increased during reconstitution. 



The susceptibility curve of the headless pieces shows an inter- 

 esting relation to that of the whole animals. In earlier stages the 



