Effect of Chemicals on Growth 509 



mecium will separate). One of a pair was put into hay infusion, 

 the other one of the pair into a ^^ NaCl solution in hay infusion. 

 It was found that all the pairs separated within 15 minutes of each 

 other, so that there is little room for error. They were allowed to 

 grow for 24 hours, and then killed and measured separately. Of 

 20 sets of pairs the results are as follows: 



Control; hay infusion; 17 dividing Para- I'g NaCl in hay infusion; 17 dividing Para- 



roecia gave 34 specimens measuring at the age mecia, mates of those in control experiment, 



of 24 hours: 213.264 ± 1.566 X 71.19. gave 34 specimens measuring at the age of 



3 dividing Paramecia gave 6 normal speci- 24 hours: 205.059 ± 2.466 X 71.64. 



mens not measured. 3 dividing Paramecia gave 6, all died. 



Taking into consideration the probable errors of the measure- 

 ments, there is evidently no significant difference in size of the 

 two sets. However, three of the dividing Paramecia in the sodium 

 chloride, after separating to form 6 specimens, died, while the 

 corresponding controls remained normal. Why six out of forty 

 in the NaCl should die, while the rest throve as well as the con- 

 trols, is difficult to explain. Possibly there is a critical early 

 period in which injury may occur; if the animals survive this, 

 they flourish. The experiment taken as a whole shows, however, 

 that the chemical is not so injurious to the young if the parents 

 have been subjected to it a short time before fission. 



Acclimatization to NaCl 



We have seen above that certain concentrations of NaCl de- 

 crease growth. It was therefore determined to cultivate Para- 

 mecia in one of these solutions, to see if a smaller race could be 

 obtained from L^, or if possible, this race might changeinto one 

 of the other races described by Jennings. » It was very easy to 

 acclimatize Paramecium to a iL NaCl solution. If introduced 

 directly into such a solution, Paramecia, as we have seen, die in a 

 few minutes. The method of procedure for producing acclima- 

 tization was as follows. Adult specimens were put into a 



'Loc. cit., page 494. 



