DEVELOPMENT OF THE BACTERIA. 125 



divides into two in the space of an hour, then in 

 four at the end of a second hour, then in eight 

 at the end of three hours, in twenty-four hours 

 the number will already amount to more than six- 

 teen millions and a half (16,777,220); at the end 

 of two days this bacterium will have multiplied 

 to the incredible number of 281,500,000,000; at 

 the end of three days it will have furnished forty- 

 seven trillions ; at the end of about a week, a 

 number which can only be represented by fifty-one 

 figures. 



" In order to render these numbers more com- 

 prehensible, let us seek the volume and the weight 

 which may result from the multiplication of a 

 single bacterium. The individuals of the most 

 common species of rod-bacteria present the form 

 of a short cylinder having a diameter of a thou- 

 sandth of a millimeter, and in the vicinity of one five 

 hundredth of a millimetre in length. Let us rep- 

 resent to ourselves a cubic measure of a millimetre. 

 This measure would contain, according to what we 

 have just said, 633,000,000 of rod-bacteria with- 

 out leaving any empty space. Now, at the end 

 of twenty-four hours the bacteria coming from 

 a single rod would occupy the fortieth part of a 

 cubic millimeter; but at the end of the follow- 

 ing day they would fill a space equal to 442,570 

 of these cubes, or about a half a litre. Let us 

 admit that the space occupied by the sea is equal 

 to two-thirds of the terrestrial surface, and that 

 its mean depth is a mile, the capacity of the ocean 

 will be 928,000,000 of cubic miles. The multipli- 



