194 SPECIAL MEDIA 



to employ an incubating temperature of 30, C., 10 per cent, 

 gelatine and o . 5 per cent, agar must be dissolved in the meat 

 extract before the addition of the peptone and salt; while for 

 incubating at 37 C., 12 per cent, gelatine and 0.75 per cent, agar 

 must be used. Avoid the addition of more agar than is absolutely 

 necessary, otherwise the action upon the medium of such organisms 

 as elaborate a liquefying ferment may be retarded or completely 

 absent. 



1. Measure out 400 c.c. double strength meat extract into a 

 "tared" 2-litre flask, and add to it gelatine, 100 grammes. 



2. Weigh out powdered agar, 5 grammes, emulsify with 100 c.c., 

 cold distilled water and add to the contents of the flask. 



3. Dissolve the agar and gelatine by bubbling live steam 

 through the flask for twenty minutes. 



4. Weigh out peptone, 10 grammes; salt, 5 grammes ; emulsify 

 with 100 c.c. double strength meat extract previously heated to 

 60 C., and add to the contents of the flask. 



5. Replace in the steamer for fifteen minutes. Then adjust the 

 weight to the calculated figure for one litre (in this instance 1120 

 grammes) by the addition of distilled water at 100 C. 



6. Estimate the reaction; control the result. Then add 

 sufficient caustic soda solution to render the reaction + 10. 



7. Replace in the steamer at 100 C. for twenty minutes. 



8. Cool to 60 C. Clarify with egg as for nutrient agar. 



9. Filter through papier Chardin, using the hot-water funnel. 



10. Tube, and sterilise as for nutrient agar. 



Agar Gelatine (Guarniari). 



1. Measure out double strength meat extract, 400 c.c., into a 

 "tared" 2 -litre flask, and add to it gelatine, 50 grammes. 



2. Weigh out powdered agar, 3 grammes; emulsify with cold 

 distilled water, 50 c.c., and add to the contents of the flask. 



3 . Dissolve the agar and gelatine by bubbling live steam through 

 the flask for twenty minutes. 



4. Weigh out Witte's peptone, 25 grammes; salt, 5 grammes, 

 and emulsify with 100 c.c. double strength meat extract previously 

 heated to 60 C., and add to the contents of the flask. 



5. Replace in the steamer for fifteen minutes. 



6. Weigh the flask and make up the medium mass to the cal- 

 culated figure for one litre (1083 grammes) by the addition of 

 distilled water at 100 C. 



7. Neutralise carefully to litmus paper by the successive 

 additions of small quantities of normal soda solution. 



8. Replace in the steamer at 100 C. for twenty minutes. 



9. Cool to 60 C. Clarify with egg as for nutrient agar. 



10. Filter through papier Chardin, using the hot-water funnel. 



11. Tube, and sterilise as for nutrient agar. 



