12 THE BACTERIA IN ASIATIC CHOLERA. [CH. 



"Comma-bacilli flourish best at temperatures between 

 30 and 40 Cent. (86 to 104 Fahr.), but they are not very 

 susceptible to lower temperatures. Experiments have been 

 made on this point, which show that they can grow very 

 well at 17 Cent., though more slowly. Below 17 Cent. 

 the growth is very slight, and seems to cease below 16. 

 In this point the comma-bacilli remarkably resemble 

 anthrax-bacilli which also have this minimum temperature 

 as the limit for their growth-power. Once I made an 

 experiment to test the influence of lower temperatures 

 on comma-bacilli, and to see if, at a very low temperature, 

 they are not only hindered in their development but also 

 if they cannot possibly be killed. For this purpose 

 an artificial cultivation was exposed for an hour to a 

 temperature of 10 Cent, below zero; during this time it 

 was completely frozen. When part of it was put into 

 the gelatine, there was not the least difference visible in 

 the development or growth, so that they bear frost very 

 well. It is not the same with the withdrawal of air and 

 oxygen. They immediately cease to grow when deprived 

 of air, and accordingly belong, if the division into aerobic 

 and anaerobic bacteria be held as good, to the aerobic class. 

 Any one can convince himself of this very simply, by laying 

 a piece of talc or mica over the glass plate, when the 

 portion of the artifical cultivation has been placed on it in 

 liquid gelatine, and when the gelatine is beginning to stiffen ; 

 the talc or mica must be as thin as possible, and must cover 

 at least one-third of the gelatine surface in the middle. The 

 piece of mica, owing to its elasticity, adheres completely 

 to the surface of the gelatine, and thus cuts off the air from 

 the portion covered. Then, as soon as the development 

 of the colonies follows, it is seen that the development only 

 takes place where the gelatine is not covered, and only a 



