36 BACTERIA, GENERAL CONSIDERATIONS, MORPHOLOGY 



give the bacillus a somewhat barrel-shaped appearance. Such a 

 bacillus is known as a clostridium. 



Sporogenous Granules. When spore formation is' about to occur 

 in a bacterium there appears in its interior, first, a dust-like trans- 

 formation of the protoplasm, which gives it a powdered appearance; 

 next appears one or more highly refractive bodies, the so-called sporog- 

 enous granules. These become confluent, and from them the spore 

 is formed as a highly refractive body, composed of condensed proto- 

 plasm, and surrounded by a very firm, tenacious, tough membrane. 

 The spore may escape from the bacillus at one end or it may rupture 

 the bacterium in the equatorial plane. When a spore is placed under 

 favorable conditions it takes up food material, its capsule ruptures, 



FIG. 22 



Bacillus subtilis sporulating. The unstained spaces in the centre of the rod are spores. 

 (Author's preparation.) 



and from its protoplasm is formed the ordinary, typical, vegetative 

 variety of the bacterium from which the spore was originally formed. 

 This process of the formation of the adult vegetative form of the 

 bacterium from its spore is called the germination of the spore. 



Arthrospores. Cocci sometimes appear to change their whole body 

 into a spore. These supposed spores were called arthrospores. 

 Our knowledge of this type is limited and requires further study, 

 but it is thought that the so-called arthrospores are merely invo- 

 lution forms. Of the disease-producing bacteria we may name as 

 examples of spore-formers the bacilli of anthrax, tetanus, malignant 

 edema, emphysematous anthrax, or black-leg; of harmless sapro- 

 phytes the Bacillus subtilis and the Bacillus megatherium. Spores 

 cannot be stained by the ordinary methods used to dye the vegetative 

 forms. 



