428 SPORE CYCLE OF BACILLUS SUBTILIS 



temperature. The time required for germination does not show this 

 acceleration, as is evident from Fig. 1. This indicates that 37° is 

 decidedly above the optimum for germination. 



The time required for the completion of the spore cycle is shown 

 graphically in Fig. 2, which indicates that the spore cycle was com- 

 pleted only at pH 5 to 10 and that the rate of completion is acceler- 

 ated by the rise in temperature. The acceleration, however, is ir- 

 regular and does not maintain any uniformity throughout the series. 

 The irregularity in the curve may be due to the previously mentioned 

 automatic adjustment of the reaction of the media during the period 

 of active growth which is included in the spore cycle. In broth of 

 pH 5,6, and 9, the hydrogen ion concentration would be gradually ap- 

 proaching the optimum during the period of active growth. 



The apparent discrepancy in pH 10 of the 25° C. is probably due to 

 the formation of spores because of the unfitness of medium of this 

 pH value for growth and multiplication. The slight difference in 

 time required for spore formation in broth of this pH value at 25° and 

 37° indicates that spore formation in this medium is probably not in- 

 duced by products of metabolism. 



SUMMARY AND CONCLUSIONS. 



1. At 5°C. no germination took place. 



2. At 25°C. and at 37°C. germination occurs if the hydrogen ion 

 concentration of the broth is kept between pH 5 and pH 10, but not 

 at higher or lower pH values. 



3. The completion of the spore cycle likewise requires a hydrogen 

 ion concentration between pH 5 and pH 10. 



4. The spores can germinate when the pH value is 10, although after 

 germination the vegetative cells multiply only to a very slight extent 

 and soon pass into spores. 



5. The slight growth and multiplication of vegetative cells in broth 

 of pH 10 suggest that the formation of endospores in this medium must 

 be caused largely by the unfavorable reaction of the medium rather 

 than by the accumulation of metabolic products. 



6. Automatic adjustment of the medium seems to play a role in the 

 completion of the spore cycle. 



7. The results are not only of theoretical importance but they have 

 a practical application to the preservation of food by canning and by 

 other methods. 



