124 PHYSIOLOGY OF THE BACTERIA. 



Under other circumstances, and probably in con- 

 sequence of a mucus transformation of the walls 

 of the mother cells, the new bacteria are envel- 

 oped by a mass of glutinous substance. We have 

 described these masses under the name of Zo- 

 ogloea. 



The conditions which favor multiplication by 

 fission are, a certain degree of temperature and 

 a sufficient quantity of nutritive material. The 

 higher the temperature, the more rapid is the 

 segmentation of the bacteria, the more rapid their 

 multiplication, — that is to say, up to a certain 

 limit, variable with the species and beyond which 

 the bacteria are destroyed. 



The multiplication decreases when the tempera- 

 ture is lower, and ceases entirely in the vicinity 

 of 0° (32° Fah.). 



The influence of richness of nutriment is well 

 seen in artificial cultivation. So long as the bacte- 

 ria find the necessary aliment, in sufficient quantity, 

 to form new protoplasm, they multiply with ac- 

 tivity ; but as soon as the organic matter is de- 

 voured, they cease to divide, fall to the bottom 

 of the vessel, where they accumulate, motionless, 

 and form a deposit more or less abundant. 



The multiplication of the bacteria by binary fis- 

 sion has for result, if nothing occurs to interfere 

 with the most favorable conditions, the invasion 

 of the medium by an incredible number of these 

 little beings, of which we can only form an idea 

 by calculation. 



" Let us suppose," says Cohn, " that a bacterium 



