TEXT-BOOK OF BACTERIOLOGY, 93 



micro-organisms will be found in it : cocci, bacilli, separate or hang- 

 ing together in long threads, but whose form alone shows them to 

 belong to different species; here and there, too, beautifully-twisted, 

 lively, motile spirilla are seen. If some of this saliva be placed 

 on our food media — for example, on bouillon gelatin — it will soon be 

 seen that very few germs develop, and that the number of colonies 

 is very much smaller than might be expected, after the number of 

 bacteria which were seen in the inoculating material under the 

 microscope. 



Though these conditions may not be found everywhere to such 

 a striking extent as in the experiment just mentioned, there can 

 be no doubt that many micro-organisms cannot thrive on our 

 culture media. 



One more point is to be noticed here. On reading a number of 

 French treatises on bacteriological subjects, passages will surely 

 be met with in which the exclusive use of liquid food media is 

 warmly recommended. 



The use of the latter is evidently considered by some of our 

 colleagues beyond the Rhine as a national affair, which, were it 

 only as a matter of patriotism, must be strongly defended against 

 German innovations. 



They maintain, for instance, that in the bouillon a great num- 

 ber of bacteria can thrive which fail to do so on a solid medium. 

 This, however, it may be positively asserted, is not tli,e case; such 

 differences do not exist, and would, indeed, be altogether incom- 

 prehensible in view of the manner in which the solid food media are 

 prepared. 



Our culture media, whether solid or liquid, are all essentially 

 similar, and the monotonous method of proceeding is doubtless 

 sometimes the cause of failures in our breeding experiments. 



It would be an interesting and doubtless profitable research to 

 study the necessary conditions of life for those bacteria which have 

 hitherto resisted all efforts to breed them. This would necessitate 

 a methodical, systematic variation of the food solutions, for with 

 many species the question of their cultivation is certainly a merj 

 question of their proper nutrition. 



V. USES OF FOOD MEDIA FOR OBTAINING AND MAINTAINING 



PURE CULTURES. 



How.are the food media to be used for obtaining and maintain- 

 ing pure cultures ? 



It will be remembered how we proceeded with the first solid 

 food medium whicfi was employed : that out of a mixture of bac- 



