18 



THE SMALLEST LIVING THINGS 



The Multiplication of Bacteria 



Bacteria raised in a proper nutrient medium reproduce rapidly 

 by simple cross division, whereby one bacterium splits into two, 

 and, by a continuation of the process, in an incredibly short time 

 great masses known as colonies are formed. "It has been esti- 



Courtcsy of Dr. Edwin O. Jordan 



Fig. 8— THE BACILLUS WHICH CAUSES DIPHTHERIA 



Left, individual cells — magnification, 1200: right, colonies grown on artificial 



medium — slightly magnified 



From photomicrographs 



mated that if bacterial multiplication went on unchecked, and the 

 division of each cell took place as often as once an hour, the 

 descendants of each individual would in two days number 

 281,500,000,000, and that in three days the progeny of a single 

 cell would balance 148,356 hundred weight!" * As a result of 



* E. O. Jordan, General Bacteriology. Such geometrical propagation is possible, 

 however, only in theory, for their own secretion products, enemies of one kind or 

 another, varying conditions of food, temperature, and culture medium, all tend to 

 check their multiplication. 



