GENERAL CHARACTERISTICS OF BACTERIA. 35 



growth and products to derangements which are known 

 as acute or chronic infectious diseases. 



Numerous attempts have been made by various 

 authors to classify bacteria systematically, but usually 

 with the proviso that the system was only a temporary 

 one. The classification of the older naturalists and 

 botanists was based generally upon purely morphological 

 peculiarities. As this depended, at times, upon slight 

 variations that were seen to occur in the size and shape 

 of one and the same species, it naturally resulted in a 

 more or less complicated arrangement. In this place 

 the morphological character of the bacteria will alone 

 be given, their classification being left until the general 

 characteristics of bacteria have been considered. 



ih 

 MORPHOLOGY. 



The basic forms of the single bacterial cells are 

 threefold the sphere, the rod, and the segment of a 

 spiral. Although under different conditions, the form 

 of any one species may vary considerably, yet these 

 three main divisions under similar conditions are per- 

 manent; and, so far as we know, it is never possible 

 by any means to bring about changes in the organisms 

 that will result in the conversion of the morphology of 

 the members of one group into that of another that 

 is, micrococci always, under suitable conditions, produce 

 micrococci, bacilli produce bacilli, and spirilla produce 

 spirilla. 



The form of the bacterial cells at their stage of com- 

 plete development must be distinguished from that 

 which they possess just after or just before they have 

 divided. As the spherical cell develops preparatory to 



