GENERAL- MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 2J 



to the belief that perhaps nearly all, if not all, micrococci and bacilli have 

 active motion under certain conditions. This makes it clear that the attempt 

 to group microbes into motile and non-motile must result in failure. The 

 attempt to make generic distinctions based upon the absence or presence of 

 few or many flagellae, upon the existence of polar or non-polar flagellae, etc., 

 is also unsatisfactory. Special staining methods are necessary to demon- 

 strate the presence or absence of flagellae. Some investigators declare that 

 it is almost impossible to demonstrate them ocularly. That they do exist is 

 fully demonstrated, but it is not demonstrated to any degree of satisfaction 

 that it is practicable to make finely drawn numerical and structural distinc- 

 tions in the flagellae of the different species of microbes. 



The rate of motion of bacteria has been measured. The cholera bacillus 

 moves at the rate of 18 cm. per hour. The typhoid bacillus is slower moving 

 a distance of 4 mm. in one hour. The rate of motion in one and the same 



< m 



Fig. 8. Illustrating polymorphism or pleomorphism. Involution forms of the bacillus of 

 Asiatic cholera. (Williams.) 



species is, however, variable, being comparatively rapid at one time under 

 certain conditions of food supply, warmth, etc., and at other times com- 

 paratively slow. 



When the microbe approaches the end of the life cycle, or when the con- 

 ditions for growth and septation are no longer good, spore formation is apt 

 to take place. This spore formation is of two kinds, endospore formation 

 and arthrospore formation. The former predominates, and occurs largely 

 in the group bacilli, though it is also noticeable among the micrococci and 

 the spirillae. Endospores are usually spherical, though they may be slightly 

 elongated, and usually occur near one end of the cell, and usually there is 

 only one in each cell. Generally the diameter of the spore is equal to or 

 somewhat less than the diameter of the cell-lumen. Sometimes, however, 

 the diameter of the spore exceeds that of the cell-lumen, causing a charac- 

 teristic bulging, as in the tetanus bacillus (drum-stick bacillus, Trommel- 

 hldger Bacillus). The spore is formed from the cytoplasm, and differs 



