6 GENERAL MORPHOLOGY AND BIOLOGY. 



being again transferred to favourable conditions, only slight 

 growth at first takes place. Many individuals have un- 

 doubtedly 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 threadlike 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 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 rodlike in shape, some- 

 times 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 proto- 

 plasm 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, No. u). In structure the spore consists of a mass 

 of protoplasm surrounded by a dense membrane. This 



