378 JULIA ELEANOR MOODY 



of senile degeneration followed by physiological death, claiming 

 that the results obtained by Calkins and Popoff were due to 

 fault}^ technique resulting in bacterial invasion of the cultures. 

 Calkins' methods, fully given in his paper of 1902, show that 

 a careful technique was followed throughout his work; the cycles 

 which he observed during the 742 generations of Paramoecium 

 must therefore have been due to a cause other than the one 

 suggested by Enriques. 



Spathidium shows a rhythmic rise and fall in division-rate 

 corresponding to the vitality of the cell and in this respect agrees 

 with the results obtained by Calkins, Woodruff, Popoff and 

 Gregory for Paramoecium, Oxytricha, Gastrostyla and Tillina. 



Reference to diagram 1 will show that Spathidium responded 

 but slightly to treatment with salts. During the period when 

 the division rate fell suddenly from 3.1 to 1.6, the cultures were 

 treated with beef extract. The curve shows only a temporary 

 response, the division-rate gradually dropping to 1.3 during 

 the eighth period. 



Artificial stimulation at this time increased somewhat the 

 general vitality, which is indicated by the higher division-rate. 

 That the effect was, however, temporary is shown by the gradual 

 downward trend of the curve, ending in the death of the series. 

 In this respect the life-cycle of Spathidium spathula closely 

 agrees with the results of Gregory for Tillina magna concerning 

 which she says: 



Unlike Paramoecium and Oxytricha, the division rate of Tillina 

 does not indicate a definite response to treatment with salts. Such 

 substances, apparently successful in other forms, seem to have been 

 effective only in raising the vitality slightly above the normal and 

 increasing it sufficiently to carry the protoplasm through periods of 

 weakness. 



Woodruff defines a cycle as ''a periodic rise and fall of the 

 fission rate extending over a varying number of rhythms and 

 ending in extinction of the race unless it is 'rejuvenated' by 

 conjugation or changed environment." The variations in divis- 

 ion-rate represented in the life-cycle of Spathidium' spathula 

 may all be interpreted as normal 'rhythms,' the entire curve 

 covering 218 generations, representing but one cycle. 



