TRYPSIN BROTH 71 



(500 grm. of meat to each litre of water), the mixture is 

 thoroughly stirred, rendered faintly alkaline to litmus, 

 and heated to 70-80 C. for five minutes. The mixture 

 is cooled to 45 C., 1 per cent, of trypsin solution (i.e. 

 40 c.c. to the 4 litres) is added (Allen and Hanbury's 

 Liquor Trypsinse Co.), and the whole is kept for two or 

 three hours at 37 C. At the end of that time, the mixture 

 is rendered slightly acid with acetic acid and then brought 

 to the boil, whereby unaltered albumin, etc., is precipi- 

 tated : the mixture is then strained through cotton -wool 

 or fine muslin. The fluid is rendered alkaline, 0-5 grm. 

 of calcium chloride and 10 grm. of sodium chloride are 

 then added and the mixture is autoclaved for an hour 

 at 115 C. This procedure precipitates phosphates and 

 the broth should now filter clear through paper. 



This broth may also be used for the preparation of 

 agar and gelatin. For agar, the agar powder should be 

 added before autoclaving ; for gelatin, the gelatin should 

 be added after autoclaving. These media are quite 

 suitable for most purposes, but in the writer's experience 

 are not so suitable for the growth of some organisms, 

 particularly some of the saprophytes, as the media made 

 with peptone. Some of the pathogenic organisms seem 

 also to die out more readily than on peptone media. 



Veal-broth. For some purposes veal presents advan- 

 tages over beef, e.g. for growing the tubercle bacillus. 

 When obtained from the butcher's the veal is frequently 

 powdered with flour ; this should be brushed and washed 

 off as completely as possible, as it renders the broth 

 turbid and difficult to clarify. The veal-broth is made 

 in precisely the same way as nutrient beef -broth. It is 

 however, often slightly alkaline, so that less alkali is 

 required for neutralisation. For the cultivation of the 

 tubercle bacillus about 4 to 6 per cent, of glycerin should 

 be added. 



