PEPTONE BOUILLON AGAR 45 



be taken that the nutrient mass be sterilised, which is done 

 by heating the filled test-tubes in the steam steriliser for 

 twenty minutes daily on three successive days. 



The tubes when filled and sterilised are laid in a slanting 

 position, for which purpose suitable contrivances of various 

 kinds are employed, the result being that the surface of the 

 agar after setting forms a very acute angle with the long 

 axis of the tube. During solidification some water, the 

 water of condensation, separates out and prevents the firm 

 adherence of the agar to the vessel, so that the medium 

 often turns if the test-tube is rotated, a phenomenon which 

 does not disappear until the water of condensation has 

 evaporated. Esmarch recommends the addition of some 

 ;i um arable to prevent slipping away from the surface of 

 the glass. 



The mass of agar is clear and transparent while liquid, 

 but after solidifying is somewhat cloudy and opaque. 



Nutrient agar is often prepared by adding 20 grm. agar, 

 5 grm. extract of meat, 5 grm. grape-sugar, and 30 grm. 

 peptone to a litre of water. Sterilisation must be carried 

 out with greater care than in the case of ordinary nutrient 

 agar, and the prepared medium is of a brownish-yellow 

 colour. 



The most varied modifications of nutrient agar can be 

 produced by the addition of solution of litmus, grape- 

 sugar, and other substances soluble in water. That most 

 commonly used is the litmus a<ir mass prepared by adding 

 40 ccm. solution of litmus to a litre of prepared agar. This 

 medium is par excellence of service in the carrying on of 

 researches on the formation of acids or alkalies during the 

 growth of micro-organisms. 



Modifications of gelatine and agar, &c. Glycerine agar 

 is often made use of, as several micro-organisms grow very 

 readily on this medium, which consists of nutrient agar 



