Chapter XIII. 



Various Kinds of Bacteria* 



The story of the bacteria is one of the most astonishing that 

 modern science has had to tell, and although they are the small- 

 est and simplest of all plants, I have thought it best to devote an 

 entire chapter to their discussion; so many are the ways in 

 which they touch human life. In these days almost everything 

 is attributed in some form or other to a microbe, and when the 

 extraordinary character of these remarkable plants is appre- 

 ciated one is not surprised to read that some savant has dis- 

 covered the microbe of crime, the microbe of drunkenness or 

 the microbe of insanity, all of which have at various times been 

 heralded by the newspapers. While crime, drunkenness and in- 

 sanity are not the result of microbe activity, yet microbes actu- 

 ally serve in a number of capacities which at first sight seem 

 quite as impossible, and one can scarcely blame the public for 

 believing, as it does, almost anything that it is told about mi- 

 crobes, or for going to the other extreme and believing nothing 

 whatever. 



What a microbe is. The term microbe, meaning "little liv- 

 ing thing," has been applied to some organisms which are not 

 bacteria, as, for example, the slime-mould-like creature which is 

 the cause of malaria, or the yeasts which have already been de- 

 scribed in the chapter upon the fungi. By far the greater num- 

 ber of microbes are bacteria, and bacteria themselves are very 

 lowly plants related to the blue-green algae, and to be consid- 

 ered, perhaps, as forms of this algal series which very long ago 

 abandoned their leaf-green and began, like the fungi, to make 

 their living in other ways. 



Classification of bacteria. In size bacteria are the smallest 

 of living things, the least of them being less in diameter than 

 one thousandth of a millimeter, so that three hundred of them 

 could stand side by side across the dot over the letter "i." Oth- 



