308 THE EXAMINATION OF MILK 



Heat in water bath for one hour, so as to dissolve the con- 

 stituents and when cooled to 50 C. add the white of an egg, and 

 heat again in water bath for i J hours ; then filter. To the 

 filtrate add : 



i gr. of lactose 



i c.c. of a .5 per cent, solution of . 



neutral-red . . . . I Pf, r Io "' of 



. . _ | the medium, 

 i c.c. of a .1 per cent, solution of 



" krystal-violet " 



Pour the medium into sterile test-tubes, 10 c.c. in each, and 

 sterilize by heating twenty minutes on three successive days. 



Melt some of the tubes in hot water, and pour the contents 

 into sterile Petri dishes. 



After the medium is set, place the dishes in the incubator 

 with the covers slightly open at- one side, so that the surface 

 may dry. 



Then take a loopful of the cultures of the diluted milk of 

 Ex. 146, in which both gas and acid production are observed, 

 and mix it with 5 or 10 c.c. of plain sterile broth; from this 

 mixture take out a loopful of the liquid and deposit it on the 

 surface of the bile-salt agar in a Petri dish ; spread it over the 

 medium by means of a sterile glass rod, bent at right angles. * 



Incubate at 37 C. for forty hours. 



Make sub-cultures of the different colonies observed upon 

 ordinary agar slopes and incubate for twenty-four hours. 



(i) Find if the organisms isolated are able to ferment 

 glucose, lactose, saccharose, dulcite, and adonite by adding a 

 loopful of the culture from the agar slope to Durham's fermenta- 

 tion tubes, containing the following broth : 



Lemco . . . .... 10 gr. 



Peptone . . . . . . 10 gr. 



Sodium bicarbonate . . ." . i gr. 



Water . . . . . . 1000 c.c. 



to which has been added i per cent, of the several carbo- 



