CHAPTER III. 

 GENERAL MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 



Bacterium (plural, bacteria) is a misleading term, though firmly estab- 

 lished in general usage. It means "a small rod," the name being applied 

 because it was believed that these minute organisms were mostly, if not all, 

 rod-shaped. This is not the case, as will be explained later. Further- 

 more, the term is used in a generic sense, and again applied to the group of 

 organisms as a whole. This causes confusion. Therefore, the generic -term 

 Bacterium is now abandoned and the term Bacillus is used to include all of the 

 micro-organisms which are rod-shaped although generic sub-divisions are 

 being made of this now very large group. The term "microbes" {micros, 

 small, and hios, life) or micro-organisms would be far more suitable than the 

 term "bacteria," as applied to the entire group of organisms included in the 

 subject of bacteriology. Microbiology is no doubt more correctly descriptive 

 than bacteriology, but the latter term is so firmly established in general usage 

 that it would be unwise to urge a change at the present time. 



Whereas the general morphology of microbes is apparently quite simple, 

 the physiology and chemistry is extremely complex, and as yet not fully 

 understood. The morphological simplicity is no doubt only apparent, and 

 not real. Perhaps, with the greater perfection of the compound microscope, 

 we may discover marked structural differences which thus far have escaped 

 our notice. 



I. Classification Of Microbes. 



Microbes are the smallest of the known living organisms. It is wholly 

 impossible to see the single individual, even the largest, with the naked eye. 

 The rod-shaped microbes (bacilli) range from o.$n to lofi in- length. Some 

 are so minute as to pass through the pores of the finest clay filters (microbes 

 of foot and mouth disease). To study them a good compound micro- 

 scope is absolutely necessary, though, as stated in the historical review 

 (Period II), Leeuwenhoek and others observed the larger forms under the 

 simple microscope. 



The systematic position of microbes has from time to time received much 

 attention. The great majority of biologists now unhesitatingly class them 

 as plants, belonging to the group fungi. It cannot be denied, however, that 

 their origin (phylogeny) is still shrouded in mystery. Some suggest that they 

 are derived from degenerate algal forms, in common with most of the fungi, 

 while others declare that they in all probability originated as microbes. A 



