STERILISED WHEY 45 



tube, and hold ready to hand. When gelatinised milk is required 

 as a medium, place one of these tubes, and a tube containing 

 5 C.C. of sterile milk, in a beaker of water. Heat up to 45", and 

 then, removing the cotton-wool plugs, quickly pour the milk into 

 the gelatine. Replace the cotton-wool plug, roll the tube in the 

 hands for a few seconds and place on one side to cool either 

 upright or on the slope as required. Exactness of measurement 

 is not necessary in the case of the milk, provided the quantit}' 

 added does not greatly exceed that of the gelatine solution. If 

 the manipulations are carefully carried out, and the tube orifices 

 flamed, there should be no fear of contamination. 



26. Sterilised whey — 



Heat a sufficient quantity (say i litre) of separated milk to 

 41° C. in a water bath.^ Make a solution of -5 of a gramme of 

 a reliable rennet powder in 100 c.c. of distilled water. Thoroughly 

 stir or agitate the mixture, and place on one side for precipita- 

 tion of the casein, which ought to take place within a few 

 minutes. Allow to stand for one hour. Filter off the clear 

 whey by means of coarse muslin, add the white of one &^^ well 

 mixed with 50 c.c. of distilled water, and thoroughly incorporate 

 by vigorous shaking. Place in the Koch steriliser and steam 

 for one hour at ioo~ C. to allow precipitation of the albumen. 

 Filter, run into test tubes and sterilise by intermittent heating in 

 the Koch for twenty minutes on three successive days. It should 

 be noted that rennet acts on casein only in neutral or acid solu- 

 tion. If, therefore, alkaline whey is desired it will be necessary to- 

 alkalinise as laid down under the reaction of media. 



27. Gelatinised litmus wJtey — 



Take whey prepared as above up to and including the first 

 filtering off of the clear whey from the precipitated casein. Allow 

 to stand in a cool place for twenty-four hours and decant ofif clear 

 supernatant liquid. Heat up to 65° C. in a water bath, and add 15 

 per cent, of gelatine cut into small pieces. When thoroughly dis- 

 solved neutralise the medium to litmus with caustic soda solution. 

 Cool down to 45" C, add the white of one e.^^ well beaten up, 

 and thoroughly incorporate with the medium. Steam in the 

 Koch at 100' C. for one hour. Filter through Chardin paper (this 

 final filtration is a somewhat tedious process), and add sufficient 



^ The optimum temperature for the action of rennet was found by Fleisch- 

 mann in his experiments to be at 41° C, but free precipitation will take place at 

 any temperature between 35° and 45° C. 



k 



