C. DOBELL 151 



(§§ 28, 36, 37) that certain chemical (and physical ?) stimuli are able 

 to increase the rate of division in " depressed " cultiires\ but similar 

 effects have also been pi-oduced in normal organisms. 



52. Peters (1904) has laid emphasis on the fact that the salt 

 content of the medium in which ciliates are cultivated is a most 

 important factor. He found as a result of numerous experiments that 

 an excess of KCl in an otherwise normal medium accelerates the division 

 of Stentor. Small quantities of chloroform act similarly upon Para- 

 mecium. 



53. Calkins and Lieb (1902) who studied the effects of alcohol on 

 "depressed" Paramecium found that this substance acts, in a certain 

 concentration, as " a continued stimulus which sustains the high rate 

 of division even during periods of depression of the control series." But 

 Woodruff (1908) has shown that minute doses of alcohol sometimes 

 increase and sometimes decrease the rate of fission. In the former case, 

 " the effect is not continuous, but gradually diminishes and finally the 

 rate of division falls below that of the control." A larger dose of alcohol 

 will again increase the rate of fission, but again for a limited period 

 only-. These results may be compared with those of Daniel (1909) 

 who finds that Stentor and Spirostomum can acquire a specific resistance 

 to alcohol — becoming " acclimatized " to small but gradually increasing 

 doses. Both Woodruff and Daniel found that alcohol-resistant ciliates 

 are more susceptible to certain other chemicals. 



54. The toxicity of certain salts to Paramecium has been studied 

 by Woodruff' and Bunzel (1909). Estabrook (1910) has studied the 

 effects of various chemicals on the growth of the same form. All the 

 substances tried^ behaved in a similar manner: " When very weak they 

 have no effect whatever. In greater concentrations, all retard the later 

 stages of growth" and cause "other injury to the organism." It is 

 surprising to find, however, that complete growth can occur in a medium 

 consisting of nothing but distilled water and a little NaCl. It may be 

 noted here that Piitter (1905) has found that Paramecium and other 

 ciliates can live for many days in distilled water containing no free 

 oxygen. 



55. Many of the earlier workers found that temperature has a 

 marked influence on the rate of fission (§ 19). All later workers have 



' And the decrease in rate of fission during "depression" may also be due to chemical 

 causes. 



- Cf. also Matheny (1910). 



^ These were NaCl, nicotine, strychnine, and alcohol, in different concentrations. 



