THE EFFECTS OF BACTERIA. Ill 



tlieir pathogenic influence, the struggle between the 

 bacteria and the tissue cells. 



All the effects of bacteria depend: (1) upon the 

 present condition of the bacteria; (2) upon the nu- 

 trient medium ; (3) upon the entrance of air ; (4) upon 

 the temperature; and (5) upon the illumination. A 

 large number of other circumstances in part less im- 

 portant, in part imperfectly known also appear to 

 play a part. 



As the most important points in reference to tem- 

 perature and illumination have already been given, 

 I will discuss chiefly the influence of the nutrient 

 medium and the entrance of air on the one hand, 

 and the composition of the terminal culture on the 

 other hand. Emphasis must be constantly laid upon 

 the latter point in order to show as clearly as pos- 

 sible how much the effects of bacteria vary according 

 as they are examined in a fully virulent zymogenic, 

 chromogenic, or pathogenic condition, or in an attenu- 

 ated condition. 



1. MECHANICAL EFFECTS. 



Under the microscope it is readily seen that many 

 bacteria exhibit a pronounced active movement, and 

 the study of flagella proves that almost all the mo- 

 tile varieties* present flagella and move by means of 

 these appendages. The movement varies greatly in 

 character; for example, creeping (bacillus megathe- 

 rium), waddling (bacillus subtilis), sinuous (vibri- 



* In the actively motile spirochsete Obermeieri and the slowly 

 creeping beggiatoa flagella have not been demonstrated, so that 

 the motion is supposed to be due to an undulating narrow mem- 

 brane which encloses the organism. 



