36 MICRO-ORGANISMS AND DISEASE [chap, 



pared and of considerable transparency. The method is 

 this : — 



Twenty grams of Aga?- strips are placed in 500 cc. of 

 distilled water in a flask to which are added 2 cc. glacial 

 acetic acid ; in this the Agar is allowed to soak and swell 

 up for fifteen to twenty minutes ; then, after pouring off, 

 it is well washed in tap-water, and finally distilled water ; 

 the fluid is well drained off. After this process the Agar 

 is easily soluble ; to it (in the flask) are now added of 

 {a) the ordinary beef broth (above stock broth) 600 cc. ; 

 this is boiled for thirty minutes, in which time all the Agar 

 has dissolved. To this solution is added the following 

 mixture (b) consisting of 400 cc. of broth, 10 grams of 

 solid peptone and 10 grams of solid salt ; the whole is now 

 made slightly alkaline with liquor potassae and clarified 

 with white of egg. After mixing well up the flask is put 

 into the autoclave and kept therein at 120° C. for fifteen 

 minutes ; it is then filtered through (folded) Chardin filter 

 on the " hot filter." This Agar broth mixture is beautifully 

 clear and limpid and filters rapidly — one liter per hour, a 

 great advantage over other Agar preparations. This 

 nutrient Agar contains then 2 per cent. Agar, i per cent, 

 peptone, i per cent, salt all dissolved in beef broth. It is 

 decanted into sterile test tubes, steamed on two successive 

 days each time for twenty minutes ; when allowed to cool 

 becomes solid. It can be solidified with slanting surface 

 by being placed on the special tray. When quite solid 

 with slanting surface a small amount of " condensation 

 water " accumulates at the bottom of the tube. 



7. Grape Sugar Gelatine and Grape Sugar Agar are the 

 media best suited as solid media for the growth of anaerobic 

 microbes. The first is the nutritive gelatine as above 

 described, sub 2, but containing 2 per cent, of grape sugar. 



