24 MICRO-ORGANISMS AND DISEASE. [CHAP. 



and hydrocele fluid can be rendered solid by exposing the 

 sterilised material (see above), in sterile plugged test-tubes, to 

 a moderate heat e.g. in the incubator at 32 to 38 C. for 

 several weeks. Through evaporation the material is rendered 

 solid. Thus treated it retains its limpidity in a perfect 

 manner. 



AGAR-AGAR, or Japan isinglass, can be obtained 1 in the 

 shape of thin transparent lamellae, or more usually as masses 

 of transparent narrow bands. For cultivation purposes the 

 following mixture is prepared : 



1. Place in a beaker Agar-Agar 10 grams, common salt 10 

 grams, distilled water 900 ccm. Dissolve over the flame and 

 boil for twenty minutes, strain, and filter through hot-filter 

 into a sterile flask plugged with sterile cotton-wool. 



It ought to be mentioned, that in all cases where any material (broth, 

 peptone sugar, nutrient gelatine, or Agar-Agar solution) is filtered into 

 a sterile flask the cotton-wool plug is taken off, and the glass tube of 

 the filter having been inserted into the neck of the flask, the cotton- 

 wool is so replaced that it well guards the mouth of the flask. 



2. Place into a clean beaker 100 ccm. of distilled water, add 

 10 grams of .peptone, and two small tins of Brand's meat 

 extract ; dissolve over flame, add liquor potassae till faintly 

 alkaline, boil, filter, and add the filtrate to the above Agar- 

 Agar solution. For the two tins of Brand's, 10 grams of 

 Liebig's meat extract can be substituted. Thus a mixture is 

 obtained which contains, besides meat extract, i per cent, of 

 Agar-Agar, i plr cent, of peptone and i per cent, of salt. 

 This is then boiled for half an hour and can be kept as stock 

 material or can be at once decanted into sterile test-tubes. 



1 Messrs. Christy and Co., of 155 Fenchurch Street, have succeeded 

 in obtaining for me large quantities of this material from Paris. I 

 understand from my friend Dr. R. Maddox that this substance is in 

 reality what the French call Gelose. 



