Il6 BACTERIOLOGICAL LABORATORY TECHNIC 



Titrate with N/20 NaOH or N/2o HC1 to match tint of stand- 

 ard tube corresponding to the Ph desired. Calculate the amount 

 of normal alkali or acid to be added to the medium to give the 

 proper reaction. 



If the natural color of the medium makes it difficult to match 

 with the standard solutions, a tube of 20 percent solution of the 

 medium in water may be placed back of the standard solution. 

 The best generally useful reaction is 7.4, a figure suitable for 

 most pathogenic organisms. 



GELATINE 



To make gelatine, bouillon is made to which gelatine is added 

 in order to render it solid. The following steps are taken: 



(a) Take a litre of water in a saucepan and add chopped beef or 

 beef extract as in bouillon. After standing overnight 

 squeeze the beef and extract the juice. 



(b) Add i percent peptone, .5 percent salt, 10 percent to 15 

 percent best gelatine and weigh. 



(c) Heat until ingredients are all dissolved. 



(d) Neutralize, gelatine is highly acid and requires much alkali. 



(e) Boil five minutes and restore weight, boil till albumin 

 coagulates. 



(/) Cool to 6oC. and add an egg well beaten up in water. 

 (g) Boil slowly till all the egg is coagulated. This clears the 



jnedium of fine particles that are not removed by filtration. 



Add .5 percent normal hydrochloric acid. 

 (h) Filter through absorbent cotton on a funnel previously wet 



with boiling water. 

 (i) Tube and sterilize in autoclave for fifteen minutes at i ioC. 



Litmus, or lacmoid, or neutral red may be added to the 



gelatine as an indicator. 



