Id8 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



{Crenothrix polyspord) (Fig. 85), an iron bacterium, which has the 

 power of oxidizing certain forms of iron, causing a deposit to accumu- 

 late in the water pipes of cities where it may cause considerable trouble. 

 It is probable also that this bacterium has had a very important part 

 in the deposition of our iron ores, such as those found on the Mesaba 

 range. Another member is the AcUfwmyces bovis (Fig. 153) -wiiich is 

 the cause of the common disease in cattle known as lumpy jaw. This 

 bacterium may also infect man. Many other forms of trichobacteria 

 are found in nature and probably play important parts in the chemical 

 transformation of matter. 



The Sulphur Bacteria. — ^The sulphur bacteria are filamentous 

 forms which may reach a length of many microns. They are cylin- 

 drical or perhaps sometimes flat. They may be either attached or 

 actively motile. The movement when present is due not to flagella, 

 but to an undulatory motion like that of the spirochetes or Oscillafia 

 among the algse. As they move forward they rotate on their own axis 

 and swing their free ends. 



Spore formation is unknown in some forms where multiplication is 

 accoinphshed by the breaking up of the threads in short segments. 

 In the case of the sessile forms conidia are produced at the end of the 

 thread and are motile (Thioihrix nivea). The sulphur bacteria contain 

 at certain stages strongly refractile sulphur granules in their bodies. 



Classification* 



The classification of bacteria was early recognized by Mueller as a 

 matter of difficulty, since he says: "The difficulties that beset the in- 

 vestigation of these microscopic animals are complex; the sure and 

 definite determination (of species) requires so much time, so much of 

 acumen of eye and judgment, so much of perseverance and patience, 

 that there is hardly anything else so difficult." Early investigators 

 found it difficult to decide whether bacteria are plants or animals, and 

 nowadays we are finding it as difficult to decide upon a system of clas- 

 sification. A great many systems have been proposed, but many of_ 

 them are untenable because those who proposed them were ignorant of 

 or unconcerned by the rules adopted by systematists in other lines. 

 The only system that seems worthy of continued life is that of Miguls^, 



• Prepared by W. D. Frqst. 



