SPORE FORMATION. 5 



globules which may be of large size. Such aberrant and degen- 

 erate appearances are referred to as involution forms. That 

 these forms really betoken degenerative changes is shown by 

 the fact that, on their being again transferred to favourable 

 conditions, only slight growth at first takes place. Many indi- 

 viduals have undoubtedly died, and the remainder which live and 

 develop into typical forms may sometimes have lost some of their 

 properties. 



Reproduction among the Higher Bacteria. Most of the higher bacteria 

 consist of thread-like structures more or less septate, and often surrounded by 

 a sheath. The organism is frequently attached at one end to some object or 

 to another individual. It grows to a certain length, and then at the free end 

 certain cells called gonidia are cast off, from which new individuals are formed. 

 These gonidia may be formed by a division taking place in the terminal ele- 

 ment of the filament, such as has occurred in the growth of the latter. In 

 some cases, however, division takes place in three dimensions of space. The 

 gonidia have a free ^existence for a certain time before becoming attached, 

 and in this stage are sometimes motile. They are usually rod-like in shape, 

 sometimes pyriform. They do not possess any special powers of resistance. 



Spore Formation. In certain species of the lower bacteria, 

 under certain circumstances, changes take place in the proto- 

 plasm which result in the formation of bodies called spores, to 

 which the vital activities of the original bacteria are transferred. 

 Spore formation occurs chiefly among the bacilli and in some 

 spirilla. Its commencement in a bacterium is indicated by the 

 appearance in the protoplasm of a minute highly refractile 

 granule (or by a number of minute highly refractile granules 

 scattered about throughout the protoplasm which gradually 

 coalesce) unstained by the ordinary methods. This increases in 

 size, and assumes a round, oval, or short rod-shaped form, always 

 shorter but often broader than the original bacterium. In the 

 process of spore formation the rest of the bacterial protoplasm 

 may remain unchanged in appearance and staining power for a 

 considerable time (e.g. B. tetani\ or, on the other hand, it may 

 soon lose its power of staining and ultimately disappear, leaving 

 the spore in the remains of the envelope (e.g. B. anthracis). 

 This method of spore formation is called endogenous. Bacterial 

 spores are always non-motile. The spore may appear in the 

 centre of the bacterium, or it may be at one extremity, or a 

 short distance from one extremity (Fig. I, No. 1 1). In structure 

 the spore consists of a mass of protoplasm surrounded by a dense 



