30 THE MORPHOLOGY OF BACTERIA 



in the center of the rod : if the spore is at one end, a drumstick-shaped 

 organism results. Usually the size and position of the spore is fairly 

 constant in a given type of bacteria. Spore formation is most common 

 among the anaerobes, fairly common among the saprophytic bacteria, 

 practically absent in the pathogenic bacteria, and practically never 

 takes place spontaneously in the human or animal body. The spiral 

 organisms rarely produce spores, and, with the exception of Sarcina 

 pulmonum, spore formation is practically never observed in the cocci. 



It has never been satisfactorily determined whether spore formation 

 is a regular definite stage in the life history of bacteria which produce 

 them or whether spores are produced rather under the stress of unfavor- 

 able evironmental conditions. 



Germination of Spores. When bacterial spores are placed in an 

 environment favorable to the vegetative activity of the cell, they 

 germinate: the dense membrane which constitutes the ectoplasm of 

 the spore softens, usually at the pole or the equator, and the vegeta- 

 tive rod emerges, at first as a small bud, then rapidly assumes the 

 typical size and shape of the fully mature cell. The development of 

 the anthrax bacillus from the spore is usually in the line of the longer 

 axis, polar germination: B. subtilis, on the contrary, usually emerges 

 at right angles to the larger axis of the spore, equatorial germination. 

 Many spores are circular in outline, and in such cases the relation of the 

 developing vegetative cell to the axis of the spore is unknown. Fre- 

 quently the remnants of the spore membrane remain attached to one 

 end of the newly formed vegetative cell, appearing as a cap, as it were. 

 Some spores do not appear to rupture as germination takes place. 

 the newly forming organism appears to absorb the entire spore and 

 its ectoplasm, incorporating the entire structure by solution in the 

 vegetative cell. 



Arthrospores. Certain organisms belonging to the coccal group, 

 more particularly the streptococci, exhibit from time to time cells 

 which are decidedly larger than their fellows. These cells are more 

 highly refractile, they usually possess a granular cytoplasm, and fre- 

 quently stain somewhat irregularly. They have been designated by 

 Hueppe as arthrospores. These arthrospores appear to have no 

 unusual resisting powers, and they are in no sense to be regarded as 

 true spores. It is very probable that they are involution forms. 



