84 BACTERIOLOGICAL ANALYSIS LESSONS 



(5) Pour it into a large flask containing 5 grammes of 

 sodium chloride and 10 grammes of pure peptone. 



(6) Heat this mixture in a water bath or in a steam 

 steriliser, at 100 C., for an hour, shaking the flask from 

 time to time, so as to prevent the peptone from being 

 charred. 



(7) Now neutralise carefully with a concentrated solution 

 of sodium carbonate, making the solution faintly alkaline. 



(Should the solution have been made too alkaline, 

 add a little lactate of ammonium, till the proper 

 degree of alkalinity is reached.) 



(8) After neutralisation, heat for another half -hour in 

 the water bath or steam steriliser, shaking the flask from 

 time to time as before. 



(9) Once more test the reaction, and if unchanged, i.e. if 

 slightly alkaline, filter into a sterilised flask through two 

 layers of Swedish filter-paper. 



(10) Sterilise on two successive days in the steamer, 

 for twenty minutes on each occasion. 1 



To fill tubes with broth : 



Take a number of cleaned and sterilised test-tubes. 



1 If after the first sterilisation a precipitate appears, or the broth 

 becomes turbid, allow it to settle ; then filter again and recommence 

 the sterilisation. If, in spite of a second filtration, the broth does 

 not remain clear, it is advisable to add the white of an egg to the 

 broth, while cool, and to heat it gradually, shaking it from time to 

 time. Heat till all the albumen is precipitated and carried down with 

 the white of egg. Then filter again, and sterilise on three successive 

 occasions. 



