CHAPTER II. 



Morphology' of Bacteria — Chemical Composition of Bacteria — Mode of 

 Multiplication — Spore-formation — Motility. 



In structure the bacteria are unicellular, always develop- 

 ing from pre-existing cells of the same character and never 

 appearing spontaneously. They are seen to occur as spher- 

 ical, rod- and spiral-shaped bodies that multiply by the 

 simple process of transverse division, belonging, therefore, to 

 the schizomycetes or fission fungi. 



In size the bacteria are among the smallest living crea- 

 tures with which we are acquainted, being visible only 

 when very highly magnified. In order that some conception 

 of their microscopic dimensions may be formed, it has been 

 computed that of the average size bacteria about thirty 

 billion would be required to weigh a gram, and that about 

 one billion seven hundred million of the small spherical forms 

 might readily be suspended in a drop of water. 



Under what we are accustomed to regard as normal con- 

 ditions of development, and by the ordinary methods of 

 examination, bacteria appear very simple in form and 

 structure. They are cells consisting of a protoplasmic mass 

 within a membranous hull that is discernible with more or 

 less difiiculty. The protoplasmic body is of material closely 

 allied, chemically speaking, to ordinary vegetable protein. 

 It is often homogenous, but in particular species and under 

 various conditions of growth the central mass in stained 



' Morphology, pertaining to shape, outline, structure. 

 (60) 



