GELATIN MEDIA 



35 



Eyre uses a soda solution of ten times normal strength, which 

 is delivered out of a 1 c.c. pipette divided into hundredths ; this 

 obviates, to a large extent, the error introduced by increasing 

 the bulk of the medium on the addition of the neutralising 

 solution. 



1 (b). Glucose Broth. To the other constituents of 1 (a) 

 there is added 1 or 2 per cent of grape sugar. The steps in the 

 preparation are the same. Glucose being a reducing agent, 

 no free oxygen can exist in a medium containing it, and there- 

 fore glucose broth is used as a culture fluid for anaerobic 

 organisms. 



1 (c). Glycerin Broth. The initial steps are the same as in 

 1 (a), but after filtration 6 to 8 per cent of glycerin (sp. grav. 1'25) 

 is added. This medium is especially used for growing the 

 tubercle bacillus when the soluble products of the growth of the 

 latter are required. 



2. Gelatin Media. These are simply the above broths, with 

 gelatin added as a solidifying body. 



2 (a). Peptone Gelatin : 



Meat extract 

 Sodium chloride 

 Peptone albumin 

 Gelatin 



. 1000 c.c. 



5 grms. 

 10 

 100-150 



(the " gold label " gelatin of Coignet et Cie, Paris, is the best). 

 The gelatin is cut into small pieces, and added with the other 

 constituents to the extract ; they are 

 then thoroughly melted on a sand bath, 

 or in the " Koch." The fluid medium 

 is then rendered slightly alkaline, as 

 in 1 (a), and filtered through filter 

 paper. As the medium must not be 

 allowed to solidify during the process, 

 it must be kept warm. This is effected 

 by putting the flask and funnel into a 

 tall Koch's steriliser, in which case 

 the funnel must be supported on a 

 tripod or diaphragm, as there is great 

 danger of the neck of the flask breaking 

 if it has to support the funnel and 

 its contents. The filtration may also 

 be carried out in a funnel with water- 

 jacket which is heated, as shown in Fig. 7. Whichever instrument 

 be used, before filtering shake up the melted medium, as it is apt 



FIG. 7. Hot- water funnel. 



