424 Louise Hoyt Gregory 



zur Zeit durchsehen brauche, was von seinen Tabellen klar ge- 

 macht ist; es ist aber auch klar gemacht, dass genau diejenigen 

 Male, da die Kulturen fiir mehrere Tage sich iiberlassen sind. 

 Depresslonen erscheinen." 



This criticism is based upon a complete misunderstanding of 

 the facts and methods. Calkins says in his studies on the Life 

 History of Protozoa I: "In my experiments one individual is 

 isolated every day or every two days .... Fresh culture 

 medium is used at every isolation, and a single specimen is trans- 

 ferred to it with as little of the old medium as possible .... 

 It does no great harm to leave the culture for a longer period than 

 twenty-four or forty-eight hours. The bacterial growth is not 

 detrimental to the Paramecium. The rate of division is, however, 

 slightly reduced on the third day, and very much reduced on the 

 fourth, while the turbidity becomes less and less. If no fresh 

 infusion is added to the slide, division stops altogether, and symp- 

 toms of starvation become evident in the Infusoria." 



Thus it is not the presence but the absence of bacteria that causes 

 a slower division rate. Periods of low vitality occurred at regular 

 intervals regardless of whether the culture had been examined 

 and changed every day, or every two or three days. Great pre- 

 caution was taken in all of the experiments to prevent contamina- 

 tion of any kind. "The more apparatus used the greater the 

 danger of injuring the cultures by deleterious foreign matter such 

 as alcohol, acids, other Protozoa, etc. To avoid untold accidents, 

 I am accustomed to wipe dry the slides, cover glasses and cover 

 glass supports, using a clean cloth which is used for no other pur- 

 pose. The same care is taken with the pipettes .... I 

 take particular care of the one used for transferring the individual 

 Paramecium from one slide to another." 



Enriques may have had some ground for criticising Popoff's 

 methods, and is right in saying "Dass die Versuche von Popoff 

 keine neue Basis fiir die Degenerationstheorie gebracht haben." 

 The criticism of Calkins' work, however, is based on a false inter- 

 pretation of the facts, and as a result, is of little value. 



The true nature of the relationship between the nucleus and the 

 cvtoplasm is still an open question. The results of Gruber, Nuss- 



