32 THE FUNDAMENTAL PRINCIPLES. 



THE SIZE OF BACTERIA. 



Bacteria require to be seen and studied by the highest powers 

 of the microscope ; they vary in size from 0.2 to 30 mikrons. 

 (A mikron is yoVo millimeter ; about -^^-^ inch.) The micro- 

 cocci have a diameter of from 0.2 to 1 mikron or more. Bacilli 

 and spirilla vary in length from 2 to 30 mikrons or more ; 

 in breadth, from 1 to 4 mikrons. The average length of 

 pathogenic bacilli is 3 mikrons. 



THE EEPRODUCTION OF BACTERIA. 



As mentioned in the foregoing paragraphs, bacteria multi- 

 ply by fission. 



I. Fission. 



In the case of cocci, the round or oval cells show a little 

 indentation beginning in the membrane at two, four, or eight 

 points of its periphery, according as the division is to occur 

 in two, four, or eight parts ; this indentation increases until 

 the original cell is divided into hemispheres, quadrants, or 

 octants, as the case may be. These parts remain attached to 

 one another until complete spheric cocci are formed from 

 each part, and they then separate or not according to the 

 nature of the bacteria. 



In some forms of diplococci, as the gonococci, complete 

 spheres are never formed, the cells remaining attached to 

 each other in pairs as hemispheres. 



In the case of nearly all bacilli and spirilla the cells increase 

 to nearly double their original size before division, and the 

 division always takes place in the direction of the length of the 

 bacterium. The daughter cell remains attached for a while 

 to its parent cell after fission is complete ; occasionally this 

 attachment persists for a long time, so that large filaments 

 consisting of a number of bacteria are formed. 



II. Sporulation. 

 1. The Endospore. 



Division by fission is the usual mode of the reproduction 

 of bacteria, but at times, depending upon various circum- 



