578 J. Frank Daniel 



seconds, while normal animals survived but 162.5 seconds — an 

 increase of resistance for the acclimatized individuals of nearly 

 2 to I. 



Experiment II. Equally satisfactory evidence of immunization 

 appeared in Stentors of this type when tested as to their ability 

 to live in stronger solutions of alcohol. In this experiment the 

 following method was used : 



Stentors of type F were kept for more than three weeks in a 

 0.5 per cent solution of alcohol. These were then put into i per 

 cent for three days. From this they were transferred after two 

 days to a 2 per cent concentration. We have already seen (p. 575) 

 that 2 per cent alcohol kills unacclimatized Stentors of this type 

 within six hours. But those transferred from the i per cent solu- 

 tion were in good condition at the end of the following day. At 

 the end of the second day the animals were still in normal condi- 

 tion. At this time fourteen of them were transferred a third time, 

 to a solution 3 per cent in strength. On the following morning 

 twelve of these were dead; two, however, were alive and swimming 

 at a rapid rate. These survived the greater part of the day. 



Thus both methods of testing show that an increased resistance 

 was produced by remaining in the weak alcoholic solution. It is 

 evident that this caused some marked regulatory change in the 

 animals by which they were better able to resist the ill effects of 

 the stronger percentages of alcohol. 



Following the same general plan we may now make a closer 

 study of both types E and F. 



Ill DETAILED EXPERIMENTS 



A Method and Technique 



Following the preliminary experiments, a second series was 

 made in which the greatest care was taken to control the possible 

 sources of error, such as evaporation and dilution of the killing 

 fluid, fluctuations in temperature and variations in the organisms 

 themselves. 



