Effect of Chemicals on Growth 



503 



the controls had increased from 50 specimens to 65. At 25 hours, 

 some of each were killed and measured. The controls measured 

 200.7 X59.4 microns; those in the salt, 181. 2 X 53.4 microns. 

 This experiment shows that il^ NaCl has a definite effect upon 

 growth, inhibiting it after 60 minutes and finally causing death. 

 It also shows that there is a great variation in the resistance of 

 the animals to this strength of the chemical, some dying in 6 

 hours while other live 30 hours. 



Growth in ^^NaCl. In i^^ NaCl we have a strength of the chem- 

 ical which may or may not affect growing Paramecia, depending 

 on the conditions. In one of my experiments, there was appar- 

 ently no effect of the salt upon the growing Paramecia at any 

 time. Those in the salt grew to the same size as the controls 

 (see table X). 



TABLE X 



Measurements of growth in ~ NaCl. 



In another experiment, under what seemed exactly the same 

 conditions as before, the ^^^ NaCl had a slight inhibiting effect 

 upon the growth. The measurements are given in table XI. 



At the ages of 90 minutes, 5 hours, and 24 hours, those in the 

 salt were shorter than the controls; sufficient numbers have been 

 taken to give the figures some weight. I have worked out the 

 probable errors for the a verges, and find that, taking three times 

 the probable error of each and substracting from the greater and 

 adding to the less, in each case we still have significant differences, 

 greater at 90 minutes and 5 hours than at 24 hours. Thus it 

 seems from the analysis of the figures that there is in this case an 



