6 GENERAL MORPHOLOGY AND BIOLOGY. 



varieties, where flask-shaped or dumb-bell-shaped individuals 

 may be seen. The regularity in structure and size is quite 

 lost. The appearance of the protoplasm also is often 

 altered. Instead of, as formerly, staining well, it does not 

 stain readily, and may have a uniformly pale, homogeneous 

 appearance, while in an old culture only a small proportion 

 of the bacteria may stain at all. Sometimes a degenerated 

 bacterium, on the other hand, contains intensely stained 

 granules or globules which may be of large size. Such 

 aberrant and degenerate appearances are referred to as 

 involution forms. That these forms really betoken de- 

 generative changes is 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. 



Spore Formation. In certain species of bacteria, and 

 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. t 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. an- 

 thracis). This method of spore formation is called endogenous. 

 The spore may appear in the centre of the bacterium, or it 

 may be at one extremity, or a short distance from one ex- 

 tremity (Fig. i, No. 1 1). In structure the spore consists of a 

 mass of protoplasm surrounded by a dense membrane. This 

 can be demonstrated by methods which will be described, the 



