The Rate of Multiplication 81 



to divide. Evidence could not be obtained that this 

 was due to any shortage of oxygen or food or any 

 chemical change in the culture medium. But the ex- 

 periments do not entirely preclude these factors, and 

 Kalmus ('29) was able to demonstrate that with less 

 soluble glass and with higher concentrations of bac- 

 teria the Paramecia divided at the normal rate. Cramp- 

 ton's effect was probably of a chemical sort, therefore. 



It was noticed by Chatton ('21) that the presence of 

 sodium bromide in the culture medium of the ciliate 

 Glaucoma caused subsequent fissions to remain incom- 

 plete. An effective procedure was to place individ- 

 uals in a 1.6 percent solution of the salt for ten minutes, 

 and then to transfer them back to the usual culture 

 medium. Certain of the individuals became double, 

 especially with respect to the micronuclei and to the 

 mouth. Such a double condition then persisted through 

 subsequent generations for at least five months. 



The exact times of the generation cycle at which 

 such treatments with sodium bromide were effective 

 were worked out upon Colpidium by Ephrussi and 

 Lwoff ('23). It turned out that two periods of sus- 

 ceptibility existed in each generation, one at the time 

 of fission and the other about half-way since the pre- 

 vious fission. 



Another method of inhibiting the completion of 

 cytoplasmic fission was worked out by Chatton and 

 Chatton ('25). When a certain strain of Bacillus coli 

 as food was given to either of two species of Colpidium, 

 two or four ciliates remained attached in the form of a 

 chain. The effect was highly specific, for other genera 

 of ciliates gave no such response. Moreover, other 

 species of bacteria as food, and even three other clones 

 of B. coli, did not produce the effect. 



Treatment with very dilute hydrocyanic acid in- 

 duced formations of multiple individuals in Parame- 



