THE LIFE HISTORY OF BACTERIA. 49 



due of the protoplasm may remain on the outside of the 

 spore. 



The spore, therefore, may be considered as the con- 

 densed cell contents. It contains all the proteins of the 

 parent cell, and, when completed, lies surrounded by an 

 aqueous liquid inside the otherwise empty shell or cell- 

 membrane. This original cell wall soon softens and dis- 

 solves and the spore is thus set free. Free spores are 

 frequently met with in about 24 hours, when the growth 

 occurs under the most favorable conditions. Usually, how- 

 ever, they are not liberated for several days. It not infre- 

 quently happens that all the cells, composing a thread, form 

 spores at the same time. In that case the bright, highly 

 refracting spores are present, one in each cell, and may be 

 compared to a string of beads. With the exception of two 

 or three doubtful cases, it may be stated as a general rule 

 that a bacillus gives rise to but one spore. Inasmuch as 

 the protoplasm of the parent cell goes to make up the 

 spore it follows that the former ceases to exist as soon as 

 the spore is fully developed. 



c 



FIG. 12. Sporulation. a First stage showing sporogenic gran- 

 ules; b Incomplete spore; c Fully developed spore. 



In a given species the spore nearly always develops in 

 the same relative position within the cell. Thus, in some 

 species the spore forms in the middle and occupies, there- 

 fore, a median position. In others it develops at the very 

 end and this position may be designated as terminal. Again, 

 the spore may be located between these positions, in which 

 case it is said to be intermediate (Fig. 13 a, 6, c). 



The form of the parent cell is very often unchanged by 

 the development of the spore on the inside. At other times 

 a slight enlargement may result in that portion of the cell 

 occupied by the spore. Sometimes this, enlargement is very 



