CHAPTER XI. 



VITAL ACTIVITIES OF BACTERIA. 



Range of activities. The study of bacteria reveals their 

 many interesting properties and numerous and important 

 natural phenomena dependent upon their activities. The 

 activities of bacteria fall quite naturally into two classes, 

 first, the power they possess of doing things themselves such 

 as motility, light and pigment production, toxin elaboration, 

 etc., and secondly, their effect upon other substances or 

 things such as the decomposition of proteid substances, the 

 fermentation of sugars with the production of acids with or 

 without gas, the absorption of nitrogen from the air, and 

 many other actions of great importance to the animal world. 

 We too often look upon bacteria as agents of destruction 

 without appreciating that it is because of their activities that 

 higher animal life is possible. In a text of this kind there is 

 space to refer to but very few of the services which these 

 minute organisms render. 



The production of specific poisons such as toxins and 

 the reactionary bodies or antibodies thrown off by the tissues 

 themselves as the result of stimulation by the toxins has be- 

 come such an important part of the subject that it is dis- 

 cussed in a separate chapter, restricting the present state- 

 ments to a brief mention of the more general activities of 

 these microorganisms. 



Motility. When certain bacteria are examined micro- 

 scopically in the living condition they are observed to pre- 

 sent pronounced independent motion. The movements of 

 these forms vary in character and are described as rotary, 

 undulatory, sinuous, wobbling, and the like. Some are very 

 active while others move sluggishly. It has been proved 

 that the motile organisms possess flagella and as already 

 stated a classification of bacteria was proposed by Messea 

 based on the number and arrangement of these filaments. 

 In many cases in a hanging drop preparation it is difficult to 



