88 BACTERIOLOGY. 



look to the reaction of the medium. If it is quite alka- 

 line, 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 

 reaction. They must be neutral or very slightly alka- 

 line. 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 ; " the 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 

 eud 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 sterili- 

 zation 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, they are usually intended to be cut in half, 



