THE LIFE HISTORY OF BACTERIA. 47 



A somewhat similar condition is observed among many 

 bacteria. The active growth stops and reproduction occurs. 

 The organism in this case gives rise to what is called a 

 spore which is the analogue of the seed of a higher plant. 

 The object of either seed or spore formation may be said 

 to be the perpetuation of the species. The plant, whether 

 Jiigh or low, when in the vegetating condition is a relatively 

 weak organism. It is readily destroyed by desiccation, 

 heat, cold and other agencies. There is need, therefore, 

 of some resistant form which will enable the plant to sur- 

 vive unfavorable external conditions. The flowering plant 

 forms its seed, whereas the flowerless plant forms the spore. 



It is evident, therefore, that bacteria may be either in 

 the actively growing, vegetating form, or in the reproductive 

 or spore form. The latter is sometimes spoken of as the 

 resting, permanent or resistant form. As will presently be 

 shown the bacillus, when it sporulates or forms spores, 

 almost invariably gives rise to a single spore. The latter, 

 in turn, when it sprouts or germinates gives rise to a single 

 bacillus. Consequently it is not proper to speak of bacteria 

 as. multiplying by spore formation. When the parent cell 

 gives rise to but one spore which in turn develops into one 

 young cell the process cannot be considered as a mul- 

 tiplication or an increase of species. Bacteria reproduce, 

 perpetuate themselves by means of spores but they multiply 

 by cell division. The vegetating cell may divide, or may 

 form a spore, whereas the spore can only germinate. 



The formation of . spores has been observed in some 

 spirals, in many bacilli but not among micrococci. The 

 vast majority of bacteria, therefore, have not been seen to 

 possess spores. From this it by no means follows that 

 these bacteria always remain sporeless. The conditions of 

 spore formation are as yet but imperfectly understood and 

 it is quite probable that many, if not all, of the bacteria in 

 which spores have not been found can give rise to these 

 bodies under the conditions which prevail in nature. The 



