MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 15 



spirilla. Lastly, we have tlie filamentous forms, which may be 

 straight, leptothrix, or wavy, spirochceta, or the wavy thread may 

 be looped and entwined on itself, spirulina. 



The term involution form is applied to certain peculiar shapes, 

 which result more especially in bacteria grown under abnormal 

 conditions. They are round, oval, pear-shaped, or club-formed 

 enlargements. 



Movement — Many bacteria are devoid of movement through- 

 out the whole of their life history. Others, during certain stages of 

 their life cycle, and possibly some forms always, are endowed with 

 locomotive power. The character of the movement is very varied, 

 and ranges from a slow undulatory motion to one of extreme 

 rapidity. Many appear to progress in a definite direction. Others 

 move continuously, first in one direction and then in another, and 

 others again seem to hesitate before altering their course. They 

 may either glide along smoothly or progress with a tremulous motion. 



FiK. 2. — Spikoch^ta feom Sewage Water, x 1200. 



They appear to be able to avoid obstacles, and to set themselves 

 free from objects with which they have accidentally come into 

 contact. Vibrios have a pecuUar serpentine movement, but other 

 forms, such as the commonly known Bacterium termo and segments 

 of spirilla, such as comma-bacilli, revolve around their long axis 

 as well as make distinct progression. The complete spirilla are 

 characterised by the famihar corkscrew movement. With regard 

 to cocci there is soine doubt as to whether they are endowed with 

 independent movement, any quivering or oscillation being generally 

 regarded as only Brownian or molecular. In some straight thread- 

 forms, which are motile, the movement is very slow and vermicular 

 in character, but in wavy threads, such as the Spirochseta plicatilis, 

 there is not only an undulatory motion, with rapid progression across 

 the field of the microscope, but if they are confined by more or 

 less debris, they give very pecuUar and characteristic spasmodic 

 movements. (Fig. 2.) 



The rod-forms of Proteus vulgaris exhibit very extraordinary 



