DISEASE GERMS n 



specific characters by which they can be differentiated 

 one from the other, independently of the fact that each 

 gives rise to a specific infectious disease. The germs 

 of Asiatic cholera and of relapsing fever are spirilla. 



All bacteria multiply by binary division that is, 

 one cell divides into two, each resembling in form 

 and dimensions the parent cell, and each in its turn 

 dividing in the same way. The rapidity of multipli- 

 cation by binary division varies greatly in different 

 species, and depends upon circumstances relating to 

 temperature, moisture, and suitable nutrient material. 

 Under favourable conditions bacilli have been ob- 

 served to divide in twenty minutes, and, as each 

 daughter cell is equal in size to the mother cell, it is 

 evident that an amount of nutrient material has been 

 assimilated during this time equal to the quantity 

 contained in the original cell. As a result of this 

 rapid development, " colonies " containing millions of 

 bacilli may be developed from a single cell in twenty- 

 four to forty-eight hours. A simple calculation will 

 show what an immense number of cells may be pro- 

 duced in this time as a result of binary division oc- 

 curring, for example, every hour. The progeny of 

 a single cell would be at the end of twenty-four hours 

 16,777,220. During the process of multiplication 

 by binary division, the bacterial cells often remain 

 attached to each other, and we may see them under 



