20 MORPHOLOGY OF BACTERIA. 



This is by no means a visionary calculation, but the actual 

 weight. 



REPRODUCTION : Bacteria multiply in two ways, by fission 

 or binary division, and by sporulation. 



When all the conditions necessary for growth are present, 

 fission progresses with astonishing rapidity. When the bac- 

 terium is ready to divide, it is seen first to increase slightly 

 in size, and then it is divided into two nearly equal parts by 

 a gradual constriction in the middle. If the separation is 

 incomplete, chains of varying length are formed. The 

 rapidity with which this phenomenon occurs is entirely de- 

 pendent upon conditions influencing the growth of the organ- 

 ism. If these conditions are favorable, millions of bacteria 

 will develop from a single organism in the course of twenty- 

 four hours. It has been estimated that if each organism 

 reproduces itself by binary division once every hour, the 

 result in twenty-four hours will be 16,777,200 individual 

 germs, or 281,500,000,000 in forty-eight hours. 



Reproduction by sporulation resembles the seeding process 

 of the higher plants. It is seen mostly in the rod-shaped 

 bacteria, especially when they are no longer purely vegetative 

 or when conditions for rapid multiplication are unfavorable. 

 Fraenkel says that sporulation is an indication of the vital 

 perfection of an organism, and not a sign of deficient nutri- 

 tion. These spores are oval or spherical, very refractive 

 little bodies which develop within the organism itself, and 

 are termed endospores. They usually develop singly, and 

 are situated either at the end or in the centre of the germ 

 (Figs. 2, 3, 4). When they are of unusually large size the 

 shape of the parent cell is changed correspondingly. Thus 

 spindles, dostridia, and drum-sticks may result. The spore 

 is set free by a degeneration of the parent germ. Spores do 

 not stain well with the ordinary methods of staining, and 

 they are also very resistant to drying, heat, light, and chem- 

 icals. These properties are due to a very thick and almost 

 impenetrable membrane by which they are enclosed. This 

 peculiar resistance to extraneous influences is of great impor- 

 tance in surgery and also in the cultivation of bacteria. It 

 will be considered more fully later. 



