92 BAOTEBIOLOG Y. 



If after filtration a fine flocculent precipitate is 

 seen, look to the reaction of the medium. If it is quite 

 alkaline, neutralize, boil, and filter again. If the 

 reaction is neutral or only very slightly acid, dissolve 

 and clarify again with egg-albumin by the method given. 



The most important point in all the media, aside from 

 the correct proportion of the ingredients, is their reac- 

 tion. They must be neutral or very slightly alkaline 

 to litmus. (See remarks on Neutralization of Media.) 

 Only a few organisms develop well on media of an acid 

 reaction. In all of the above media the meat-extracts 

 now on the market may usually be substituted for the 

 meat itself in preparing the bouillon. They may be 

 employed in the proportion of from two to four grammes 

 to the litre of water. 



Preparation of Potatoes. — Potatoes are prepared 

 for use in two ways: 



1. They are taken as they come to the market — old 

 potatoes being usually recommended, and carefully 

 scrubbed under the water-tap with a stiff brush until 

 all adherent dirt has been removed; 'Hhe eyes " and all 

 discolored or decayed parts are carefully removed with 

 a pointed knife. They are then to be placed in a solu- 

 tion of corrosive sublimate of the strength of 1 : 1000 

 and allowed to remain there for twenty minutes; at the 

 end of this time, without rinsing off the sublimate, they 

 are placed in a covered tin bucket with a perforated 

 bottom and sterilized in the steam sterilizer for forty- 

 five minutes. On the second and third days the steril- 

 ization is repeated for fifteen to twenty minutes each day. 

 They must not be removed from the sterilizing bucket 

 until sterilization is complete. At the end of this time 

 they are ready for use. When prepared in this way 



