METHODS OF STUDYING BACTERIA 35 



others. This is not a reproductive process, but a protective 

 and resistant one, whereby the protoplasm or living substance 

 of the bacterium becomes condensed and surrounded by a thick 

 capsule-like condensation or cell-wall. Such spores, or endo- 

 spores, to give them their full name, can live without food or 

 water for long periods sometimes for many years and can 



1 1 II a 990 ////// 



a. b. 



FIG. 10. (a) Spore Formation in Anthrax - 

 (e>) in Tetanus Bacilli. 



even resist boiling and strong disinfectants for a considerable 

 time (see under " Sterilisation " p. 26). 



Somewhat analogous protective and highly resisting stages 

 may occur in Protozoa (encystment, etc.), and even higher up 

 the scale, e.g. in the case of certain parasitic worms. When 

 the bacterial spores find themselves again in congenial sur- 

 roundings, e.g. in suitable conditions 

 as regards food -supply, moisture, and 

 temperature, they can then germi- 

 nate, i.e. the spore-capsule bursts like 

 a seed-cover, and the contained germ 

 of protoplasm escapes and re-grows 

 into the ordinary or " vegetative " 

 type of organism from which it arose. 



. 11. Glass Flasks plugged 

 with cotton- wool. These 

 are used for the making 

 of 



The Artificial Cultivation of Bac- 



teria. One of the most important 

 methods of studyingbacteriaistogrow 

 them artificially in or upon various 

 suitable nutrient culture-media. 



Many different culture-media are employed. Some bacteria 

 will grow in a medium containing the chemical elements of 

 their protein constituents (i.e. the elements of which their 

 protoplasm is composed, such as carbon, hydrogen, oxygen, 

 nitrogen, etc.), in solutions of acetates, and other organic salts. 

 Usually various animal fluids, either natural or prepared, are 

 employed for example, blood-serum, milk, meat-broth, or 

 bouillon. Meat-extract is the commonest basis employed, and 

 as in its preparation some important constituents of the 

 animal tissues from which it is made are lost, e.g. some of the 

 salts and proteins, these are usually replaced by the addition 



