772 BACTERIA 



The spores are usually produced under conditions which are 

 unfavourable to the vegetative development of the bacteria, such 

 as want of food and water, unsuitable temperature, excess or 

 deficiency of air, and other adverse circumstances. In their 

 formation, the protoplasm shrinks away from the cell-wall 

 and surrounds itself with a more resistant and firmer mem- 

 brane, after which the old cell-wall disappears by solution 

 or breaks up and sets free the spore. One spore only is 

 usually produced at the end or in the middle of each single 



bacterial cell, and appears 

 as a round or oval body, 

 with highly refractive cell- 

 contents. In some instances 

 the mother-cell at the time 

 /■^^ of spore-formation under- 



FlG.'.63.-,. Bacterium^showlng beginning of gO^S a chaUge Of form, be- 



spore formation, completed in 2. 3- Chain of coming Spindlc-sliaped ES 

 bacterial cells in each of which spores have been or i 



produced. 4. Forms of Clostridium cells with jn Clostridiu77l (4, Fig. 262) 

 spores. 5. Drumstick-shaped bacteria with spores ^ . 



at one end. 6. Bacteria with cilia. Or shaped like a drUm-Stlck 



as in the tetanus bacillus (s, Fig. 262). 



The spores are capable of resisting without injury high tem- 

 peratures, and solutions of disinfectants which would kill the 

 bacteria in a vegetative state ; moreover, like the seeds of higher 

 plants, they often retain their vitality for many years. 



When placed under favourable conditions of temperature and 

 in suitable solutions the spores germinate. At first water is 

 absorbed and the spore enlarges and loses its brilliant appear- 

 ance : sometimes the whole spore became gradually transformed 

 into a new vegetative cell (1,2, Fig. 263), while in other cases its 

 membrane opens at the end or near the middle as at 5, Fig. 263, 

 and the protoplasm surrounded by a thin cell-wall makes its 

 exit in the form of a more or less elongated rod which soon 

 commences vegetative division. 



Some of the vegetative cells of certain bacteria are capable of 



