XII. SPECIAL MEDIA. 



In this chapter are collected a number of media 

 which have been elaborated by various workers for 

 special purposes, grouped together under headings 

 which indicate their chief utility. In many instances 

 the name of the originator of the medium is given, but 

 without reference to his original instructions, since 

 these are in many cases inadequate to the require- 

 ments of the isolated worker, who would probably fail 

 to reproduce the medium in a form giving the results 

 attributed to it by its author. Such modifications 

 have therefore been introduced as make for uniformity 

 between the different batches of media. 



A considerable number of coloured media, chiefly in- 

 tended for work with intestinal bacteria, have been 

 included ; but beyond the fact that the author's modi- 

 fication of the Drigalski-Conradi medium has been in- 

 cluded amongst the routine media of the laboratory, 

 no comment has been made upon their relative values, 

 since only by observation and practice can the skill 

 necessary to utilise their full value be acquired. 



The instructions as to sterilisation are raiely given 

 in full; the routine method of exposure in the steam 

 steriliser at 100 C. (without pressure) for twenty min- 

 utes on each of three successive days for all fluid 

 media, and thirty minutes on each of three successive 

 days for all liquefiable or solid media must be carried 

 out ; and only when these general rules are to be de- 

 parted from are further details given. 



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