156 TECHNOLOGY OF BACTERIA. 



As in other branches of science, progress has to 

 a great extent been dependent upon improvements 

 in technique. These relate especially to methods 

 of cultivation, and to the staining, mounting and 

 photographing of bacterial organisms. 



The object of the present chapter is to give as 

 concise an account as possible of the technology 

 as at present perfected, and as employed by the 

 most successful modern investigators. 



1. METHODS OF CULTIVATION. 



For the solution of many problems relating to 

 the life-histories and physiological functions of the 

 various species of Bacteria, it is essential that 

 a " pure culture " be obtained and maintained 

 through successive generations by the inoculation 

 of fresh portions of a suitable culture-medium. 

 Evidently this requires not only pure stock to 

 commence with, but also a culture-medium free 

 from living organisms sterilized, and the ex- 

 clusion of floating atmospheric germs. 



Methods of Obtaining Pure Stock. Various meth- 

 ods have been devised for the purpose of isolating 

 a single species when mingled, as is commonly the 

 case, with many others. Lister proposed to ac- 

 complish this by diluting the material containing 

 a number of distinct species e. g. a drop of 

 human saliva or of broken-down beef tea which 

 has been freely exposed to the air with a steril- 



