Communications. 323 



light coming on the object in the direction of the arrow. No. 5, 

 the same body moved at right angles, with cilia invisible. No. 6 

 represents a bacterium with one cilia moving ; as the ends a, ^, 

 were in focus the cilia were visible but not with c, d. No. 7 gives 

 their true form, and No. 8 shows the form before cilia were brought 

 into view and gives the pointed termination of the bodies. 



The spore form of development has been mentioned, but this is 

 only one of the forms in which it multiplies, and that, too, much 

 the least rapid. The most rapid increase in numbers in its local 

 development is in the growth and division of the adult cell, or 

 by fission as it is termed. " When the bacterium has grown to 

 perhaps double its original size, then it constricts itself in the 

 middle like a figure eight, and breaks into two new individuals ; 

 each of these in a short time divides again, and on account of the 

 rapidity of this process we usually find them multiplying, either 

 constricted in the middle, or hanging together in pairs. The 

 warmer the air, up to nearly 100'', the faster proceeds the division, 

 and the stronger the multiplication ; in a lower temperature it 

 becomes slower, and ceases entirely in the neighborhood of the 

 freezing point We know that bacteria divide themselves in the 

 space of an hour into two parts, then again after another hour 

 into four, after three hours into eight, etc. After twenty-four 

 hours the number exceeds sixteen and a half millions (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 increased to forty-eight trillions; and after a week 

 the number can only be expressed by figures of fifty-one places. 

 In order to make this number comprehensible, we will reckon the 

 mass which may result from the multiplication of a single bacte- 

 rium. A single individual of the most common species of Bac- 

 terium termo has the appearance of a short cylinder of a thousandth 

 of a millimetre in diameter, and perhaps one five-hundredth of a 

 millimetre in length. Let us now think of a cube, the side meas- 

 uring a millimetre (cubic millimetre), six hundred and thirty-three 

 millions of rod bacteria will completely fill this cavity without 

 leaving any empty space. The fortieth part of a cubic milli- 

 metre would perhaps contain the bacteria that proceed from one 



