154 PUBLIC HEALTH BACTERIOLOGY 



solution, place in tubes, and put in Durham's fermentation 

 tubes. Steam for 45 minutes on two successive days. 

 Double strength is also used. In tubing put 10 c.c. 

 of single strength, 10 c.c. of double, and 50 c.c. of triple, 

 into suitable tubes. To these are added respectively I c.c., 

 10 c.c., and 100 c.c. of the water sample. 



Bile-salt Neutral-red Lactose A gar is composed of agar 

 20 grm., peptones 20 grm., lactose 10 grm., bile-salt 

 5 grm., neutral-red aqueous sterile solution (i per cent) 

 4 c.c., and water to I litre. Dissolve the agar, peptones 

 and bile-salt in 500 c.c. of water by heating in the steamer 

 for 90 minutes. Add rest of water, cool to 60 C., add the 

 white of one egg, heat in steamer for 45 minutes, filter 

 through a moistened Chardin filter-paper in a warm filter- 

 jacket, heat filtrate in steamer for 15 minutes, add lactose 

 and neutral red, put in tubes, and steam for 30 minutes 

 on two successive days. The medium requires no alkali. 



Other Media. 



Milk. Fresh milk free from preservatives, with the 

 cream removed, and giving an amphoteric reaction to 

 litmus, is poured into tubes and heated in the steamer for 

 three successive days at 100 C. (Above 110 C. browns 

 it.) To prove sterility, incubate for at least three days at 

 37 C. before using. 



Litmus Milk. Add sufficient litmus to colour. 



Potato. Scrub and wash a potato ; bore a cylinder- 

 shaped piece ; split it diagonally and put each half into a 

 sterile tube, with a pad of wool at the bottom, and half an 

 inch of aq. dest. Plug, and sterilize at 100 C. on three days. 



Blood Serum. Collect blood in a sterile cylinder and 

 allow to clot. Set aside for twenty-four hours in an ice 

 chest. Pipette serum into tubes and place these in a 

 sloping position in inspissator at 75 C. for one hour. 

 Repeat on two successive days. When cool, incubate 

 for twenty-four hours at 37 C., and if no growth, they may 

 be considered sterile. 



Litmus Whey (Petruschky's). Mix milk with equal 

 quantity of water, heat to 40 to 50 C., and add dilute 

 HC1 to precipitate casein. Filter, neutralize with NaOH, 

 and heat for one or two hours in steamer, filter till 



