386 DONNELL BROOKS YOUNG 



or less normal form. Therefore, such a substance is not formed 

 by the micronucleus and stored in it until the time of division 

 when, by the chanp;es in the micronucleus, it is liberated. Rather 

 it indicates that such an hypothetical substance formed while the 

 micronucleus is present accumulates in increasing amounts in 

 the protoplasm up to the time of division when it is used up in 

 the regeneration of those parts which have to be formed anew. 

 In starved cells it w^ould appear that this substance is not formed 

 as rapidly as in normal individuals, indicating that it depends on 

 the taking in and assimilation of food. 



Just what the nature of this hypothetical substance is is doubt- 

 ful. Meyer ('04) described a substance which he discovered 

 first in Spirillum volutans and w^hich takes nuclear stains, al- 

 though it is not chromatin. He believes this substance, which 

 he calls volutin, to be a reserve of nuclear material. This has 

 been found in many other bacteria, in yeast, and in the group of 

 the flagellates. Reichenow ('09) demonstrated that volutin is 

 a nucleic-acid combination and that as the chromatin in the 

 nucleus increases, the volutin decreases in the cytoplasm; also 

 that when the nucleus is not growing the volutin increases. 

 I have not been able to demonstrate the presence of volutin in 

 Uronychia, but it or some similar substance would explain the 

 action of regeneration; that is, the nuclear reserve would be 

 used up during cell division, and as a result the ability to regen- 

 erate would be at a low ebb immediately after division. As 

 the growth processes go on, a new supply of the reserve substance 

 would form, and thus the power of regeneration would increase. 



Lund ('18) has carried out a series of experiments showing 

 that the resistance of Paramecium caudatum and Didinium 

 nasutum to KCN varies according to the age of the cell. She 

 states that the resistance of Paramecium to KCN '^when allowed 

 to feed on bacteria, showed a marked increase, and when fed 

 on yeast the resistance increases to a smaller degree, from the 

 time of division up to the following division." "When Para- 

 mecium and Didinium are prevented from obtaining food the 

 resistance to KCN gradually decreases below its value at the 

 completion of division." These differences in resistance are 



