12 TEXT-BOOK OF BACTERIOLOGY. 



are connected not only with the origin of the spores, but also with 

 the presence of nuclei in the cell protoplasm. 



How far these statements and their application may be correct 

 cannot, as yet, be definitely stated. It is a fact, however, that the 

 fully-formed spores are very differently sensitive to staining than 

 the rest of the cell, and may be very clearly distinguished from it 

 by the color alone. 



An important part of the spore is its membrane, the spore-skin. 

 This is an extremely tough and strong covering, inclosing the spore 

 on all sides and surrounding it with an almost impenetrable mantle. 



If we bring spores into a fresh nourishing solution, they germ- 

 inate sooner or later and grow into rods. This process has been 

 carefully watched (by Prazmowski and De Bary) and many impor- 

 tant things discovered. A spore about to germinate first stretches 

 somewhat in the direction of its length, its contents lose part of 

 their bright gleaming, and the dark outline — the tough membrane 

 — seems to swell. The more the spore lengthens, the more it re- 

 sembles a short cylinder. At last the membrane bursts, and a 

 young bacillus is set at liberty. The empty membrane soon dis- 

 solves and disappears. 



The formation of spores has been seen with certainty only in 

 several bacilli and some few spirilla, while in the micrococci certain 

 indications of a similar process have been observed, but no decided 

 results have as yet been obtained. 



Under what particular conditions a bacterium proceeds to spor- 

 ulate is by no means certain. Formerly it was believed that the 

 micro-organisms began sporulation as soon as the necessary condi- 

 tions for their growth were withdrawn, either by the nourishing 

 solutions being exhausted or by accumulations of their own excre- 

 tions rendering their growth and propagation more difficult. 



It has been claimed that a bacillus which fthds itself, and there- 

 fore its species, threatened with extinction, tries to avoid this by 

 being changed into the form of a spore capable of resisting most 

 external influences and waiting for better days. 



Beautiful as is this thought, the facts do not bear it out, since 

 we find bacteria forming spores when their nourishment is more 

 than sufficient. 



It is, on the other hand, very probable that the bacteria, con- 

 trary' to the higher plants, proceed to sporulation chiefly or only 

 when the cells have obtained their highest development, when they 

 are in the best conditions as regards nourishment and growth. 



The anthrax bacillus, for example, produces no spores at a tem- 

 perature of 20° C, but produces them most rapidly and certainly at 



