SPOKE FOKMATION 5 



does not stain readily, and may have a uniformly pale homo- 

 geneous appearance, while in an old culture only a small 

 proportion of the bacteria may stain at all. Sometimes, on the 

 other hand, a degenerated bacterium contains intensely stained 

 granules or globules which may be of large size. Such aberrant 

 and degenerate appearances are referred to as involution forms 

 (Fig. 1, t\ t 2 ). That these forms really betoken degenerate changes 

 i9 shown by the fact that, on their being again transferred to 

 favourable conditions, only slight growth at first takes place. 

 Many individuals 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 

 hy 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 element 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 protoplasm 

 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 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, s). In structure 

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

 membrane. This can be demonstrated by methods which will 



