48 CELL STRUCTURES 



some spores require several hours' boiling. The same rela- 

 tion holds with regard to drying, the action of chemicals, 

 light, etc. This resistance explains why it happens that 

 food materials boiled and sealed in cans to prevent the 

 entrance of organisms sometimes spoil. The spores have 

 not been killed by the boiling. It explains also in part the 

 persistence of some diseases like anthrax and black leg in 

 pastures for years. 



From the above description it follows that the spore is to 

 be considered as a condensation of the bacterial protoplasm 

 surrounded by an especially thick cell wall. Its function is 

 the preservation of the organism under adverse conditions. It 

 corresponds most closely to the encystment of certain 

 protozoa — the ameba for example. Possibly the spore 

 represents a very rudimentary beginning of a reproductive 

 function such as is gradually evolved in the higher thread 

 bacteria, the fission yeasts, the yeasts, the molds, etc. Its 

 characteristics are so markedly different, however, that the 

 function of preservation is certainly the main one. 



It must not be supposed that spores are formed under 

 adverse conditions only, because bacteria showing vigorous 

 growth frequently form spores rapidly. Special conditions are 

 necessary for their formation just as they are for the growth 

 and other functions of bacteria (Chapters VI and VII). 



