2O4 LOUISE H. GREGORY. 



and in every case the result was one of depression and a lowering 

 of the vitality. Series 61 taken from Columbia stock in the 

 250th generation was depressed to such an extent in the beef- 

 flour medium that its division rate was cut from 16.4 divisions in 

 ten days to 7.6 divisions in ten days and during the next ten day 

 period the series died w^hile the control was dividing normally. 

 Series 69 was treated for 40 days when the protoplasm was from 

 1 75-335 generations old, and at no time did the division rate of 

 the beef series equal that of the control, the average rate per line 

 for each ten day period being 9.8 divisions while that of the 

 control series was 14.5. divisions. Series 95 failed to show 

 indications of age until the 23Oth generation when the beef series 

 divided in ten days on an average of 3.2 divisions less than the 

 control. When this same series was again placed in the beef-flour 

 medium in the 3ioth generation, the division rate fell to 6.0 

 divisions per line less than that of the control. Series 97 was 

 tested for its reaction to beef six times in its life history and after 

 the initial depression in the period of youth, the vitality was not 

 lowered until the 26oth generation. From this age on, there was 

 a definite slowing of the division rate for the beef, flour series. 

 Series 61, 69, 77, 88 w r ere all old series when taken from the 

 Columbia stock so there was no opportunity to test them when 

 younger. In their old age however, they gave the expected 

 response to the beef-flour treatment. 



A comparison of the results of these three sets of experiments 

 indicates that the protoplasm of Uroleptus responds in a definite 

 manner to treatment with beef according to its age. The very 

 young individual apparently does not adjust its self to the new 

 medium, its metabolic processes are retarded and its vitality 

 lowered. At a later stage in its 'life history it is able at least to 

 adjust itself to the change in medium and to maintain a vitality 

 as great as that of the control. Then appears an age when it is 

 not only able to adjust its self to new conditions but is stimulated 

 by them and shows an immediate definite increase in its division 

 rate. Finally with age there is again a lack of adjustment 

 indicated by the lowering of vitality and slow division rate. If 

 the series is very old the substitution of the beef is sufficient to 

 cause the death of the race. 



