STIMULATING EFFECTS OF CROWDING 



175 



large volumes, f| cc, such acceleration does occur; with still larger 

 volumes we begin to see that the effect is in reality a relationship be- 

 tween the mass of animals and the mass of culture media. Inocula- 

 tions similar to those made above, but made into 40 drops of me- 

 dium, showed in 48 hours some evidence of acceleration of division 

 rate with an initial seeding of 4, but with this volume 2 individuals 

 reacted as did i. Whatever the process of conditioning the medium, 



TABLE XI 



Showing the Effect of Double Washing and Transfer of 



Paramecia to 20 Drops of Unalkalized Bacterized Medium 



(From Petersen) 



2 were no more effective in 48 hours with 1.67 cc. of medium than 

 was a single individual, while 4 were significantly more effective than 

 either. These results are exhibited in detail as Table XII. 



When the numbers produced in 20-drop cultures initially contain- 

 ing I and 4 individuals are examined by Student's method for de- 

 termining the statistical value of paired experiments, one finds, if all 

 of Petersen's comparable data are considered, that there are 2 

 chances in 10,000 of obtaining so great a deviation from the mean by 

 random sampling. When the similar data for the 40-drop cultures 

 are similarly considered, the probability, even from this short series 



