INTRODUCTION. 13 



rod-shaped or curved bodies, which may be likened to so 

 many periods, dashes and commas. It is at once perceived 

 that each bacterium is an individual by itself, and that it 

 consists of a single cell, not of an aggregation of cells, as 

 do most of the common plants and animals. 



Under favorable conditions bacteria may be seen to mul- 

 tiply, one organism being divided by a partition into two 

 parts, which separate and become two new organisms. 

 The process is called fission. 



At times certain bacteria present little bright spots which 

 enlarge, and from which the rest of the cell breaks away 

 in fragments. The bright body that remains is called a 

 spore, and has greater resisting power against injurious 

 influences than has the fully developed organism. To this 

 extent these spores are something like the seeds of higher 

 plants. There are spores that can withstand boiling for 

 hours, but fortunately that is not true, as far as we know, 

 of the spores of any of the bacteria that produce disease. 

 The earlier investigators observed the appearance of bac- 

 teria in nutrient infusions which they had endeavored to 

 sterilize by heat. They looked upon this fact as indicating 

 the possibility of spontaneous generation, and it furnished 

 the chief support of that theory. Probably their fluids 

 contained very resistant spores, and were in reality not 

 sterile. 



From these facts, a definition for bacteria may be formu- 

 lated. 



Bacteria (Greek paxTijpeov, meaning a little stick) are ex- 

 tremely minute, unicellular plants, which have no chloro- 

 phyll, and zvhich divide by fission. They are sometimes 

 called schizomycetes. In every-day language they are 

 known as microbes, and also as germs. They are gener- 

 ally classed with the fungi. In some respects they seem 

 quite closely related to the algae or simplest green plants, 



