PEPTONISED MEAT JELLY. 73 



water to the solid residue in the cloth, and express all moisture 

 from the mass once more, adding sufficient of the liquid thus obtained 



Fig. 31. — Screw press for extracting meat infusion for Koch's jelly. 



to make up the bulk of the broth to two litres. Put the two litres of 

 broth in a four-litre flask, and add to it 100 grammes {i.e., five per cent.) 

 of best table gelatine, 10 grammes (o - 5 per cent.) of dry albumen 

 peptone, and 5 grammes (0-25 per cent.) of common salt. The fine 

 photographic gelatine now so much in use is not suitable for the 

 purpose, as it does not give the requisite solidity, unless used in a 

 much larger proportion. The gelatine must be of the best French 

 variety (blue and gold label), prepared by " The Gelatine Manufac- 

 turing Company," Paris. The gelatine mixture is now stirred, and its 

 reaction tested. This is nearly always found to be distinctly acid, which 

 is not favourable to the growth of most organisms. 1 If the mixture be 



1 Certain genera (moulds) grow best in slightly acid solutions ; others (e.g., 

 Bacterium termo and its congeners) in an alkaline solution ; and others (chiefly 

 the group of micrococci) in neutral solutions. 



