Immunity of Lower Organisms to Ethyl Alcohol 589 



Stentors of this type with a normal resistance averaging 153.5 

 seconds show in a 0.5 per cent solution a gain in resistance which 

 though slight is nevertheless constant and typical. In a i per 

 cent medium the resistance is increased to 229.5 seconds. Al- 

 though the experiment was selected as one giving low results for 

 the type, nevertheless it denotes for the animals of the i per cent 

 solution a substantial gain over animals both of the control and 

 of the 0.5 per cent medium. 



But the point of most interest is that the two media, though 

 differing but slightly in strength, show a corresponding difference 

 in degree of immunity. From this it is seen that subjection to 

 two media of different strengths for a definite time gives corre- 

 sponding differences in the increase of immunity. 



Time as a Factor in the Degree of Immunity Produced. We 

 have now established two points. These are that at the end of 

 four or five hours immunity normally begins and that at the end 

 of the fourth day this is definite and considerable. The progress 

 from the one to the other may now be noted. 



The difference in degree of adjustment due to the same medium 

 at the end of a few hours and again at the end of a few days, shows 

 that immunity increases as the period in the acclimatizing fluid 

 is lengthened. This is true, however, for only a hmited time. 



In an acclimatizing medium of average strength the adjustment 

 which as we saw comes on at the end of the first few hours has by 

 the end of the first day become sufficiently clear not to be mistaken. 

 As an example of this and its subsequent history a test series may 

 be given, which gave the highest immunity found for the type. 

 In this the animals had at the end of the first day a resistance of 

 166 seconds. The resistance had on the third day increased to 

 249 seconds. On the fourth day a notable rise was shown in 

 which the killing time for the acclimatized organisms reached a 

 maximum of 334 seconds, the control at the same time showing 

 a resistance of 160 seconds. 



By the fourth day in this and subsequent experiments it was 

 found that immunity had reached a high degree of constancy. 

 For this reason, in the following experiments on this type, the 

 fourth day has been selected as the time at which tests requiring 

 a maximum degree of immunity were made. 



