172 



CHARLES PACKARD. 



In the following experiments the radium amounted to 25 mg. of 

 element. The cells were exposed in the same manner as before, 

 then stained in neutral red and destained in 11/1280 NH 4 OH. 

 The accompanying figure shows the results of experiments per- 



Hours 

 2 



of Radiation 

 34 



O 



-7 



T> 



OJ 



^6 



3 



1 54 



L 



5 

 4* 



Control 



Cells 



TEXT-FIGURE 2. The effect of radiations on permeability. 



formed in one day. It is necessary to make many tests within 

 the limits of a few hours for the cells vary somewhat in their 

 reactions to these manipulations with changing conditions of 

 food, etc. By using two tubes, each amounting to 25 mg. of 

 element it was possible to perform two experiments simultane- 

 ously and thus make seven or eight determinations in a single 

 day. The temperature in these tests remained uniformly .it 

 22 C. 



The control cells showed a slight increase in permeability after 

 remaining in a small drop of culture medium for some hours. 

 This however is not significant, for cells left as long as eight 

 hours show practically the same reaction to ammonia as those 



