METHODS OF RESEARCH: PREPARATION OF CULTURE MEDIA 107 



have toward such media in quite different manners. Cohn's 

 solution, Uschinsky's solution, Fermi's solution and Meyer's 

 solution are examples of such media; for the preparation of these 

 and others consult ''Bacteria in Relation to Plant Diseases," 

 Vol. I and the various text books. 



Pure Chemicals. — The best quality of everything, without 

 regard to expense, should be the rule. Especially in the prepa- 

 ration of synthetic media and in fermentation studies must 

 absolute purity of the chemicals be assured. Pure sugars and 

 alcohols, in particular, are difficult to obtain, and expensive. 

 Rare sugars are now to be had in this country from Digestive 

 Ferments Co., Detroit, Mich., and the Special Chemicals Co., 

 Highland Park, Chicago, 111. 



TECHNIC OF ISOLATION 



I have said so much on this subject under the different dis- 

 eases in Part III, that not much need be said here, particularly 

 if the student reads carefully what is said on this subject in the 

 various text books recommended for his perusal on page 76. 



Fire. — ^This is a very certain method for disposing of trouble- 

 some bacteria and is often resorted to by the bacteriologist. 

 "Flamhez vos vases, flambez vos vases!" cried Pasteur on a memo- 

 rable occasion. With the same end in view, flame, or burn 

 lightly with a hot spatula, the surface from beneath which you 

 wish to take material for a transfer. A little experience will 

 be more useful to you than many words. You should aim 

 to scorch the surface without cooking the interior. It is best, 

 however, to err on the side of underheating. 



Autoclave all discarded culture dishes before the glassware 

 is handed over to the servant to be washed. 



Germicides. — Certain chemicals, in another way, bring 

 about the same result as fire. Often, however, I use these 

 substances so that they act only as antiseptics. How long they 

 may be allowed to act and how strong they may be used, de- 

 pends on the nature of the germicide, and on the character of the 

 tissues exposed to it. We use about the laboratory commonly 

 only two germicides, 1 : 1000 mercuric chlorid water, and 5 



