DEVELOPMENT AND COMPOSITION OF BACTERIA 13 



hours or days, a mass of cells, or colony, will often 

 be seen with the naked eye. In different species 

 these colonies are often strongly characteristic, 

 varying with the culture media and the conditions 

 under which they are grown. 



Besides shape, size, and general appearance, 

 color is often a characteristic difference; but while 

 these differences are important, bacteriologists do 

 not rely upon observations made with the naked 

 eye (macroscopic). 



" The attempt to determine species of bacteria 

 by ordinary macroscopic methods leads to difficul- 

 ties of the same kind as would be met if we tried 

 to differentiate species from the marks presented 

 by masses of trees in forests from a distance — 

 say, in a balloon. A forest of a given species of 

 tree would appear different at different seasons, and 

 according to its age, the kind of soil, climate, and 

 so on, and the treatment it had received previous 

 to planting." (Marshall Ward.) 



The Chemical Composition of Bacteria.. — The 



jw^lgg r»f hnpfpria. fl-cp-^^ada, np-^f ahout-Sn per 



. cent of wa ter, the amount varying with the species 

 and the nature of the culture medium; the usual 

 analysis being: 



