LABORATORY WORK IN* DAIRY BACTERIOLOGY 283 



I 



at any time. But when the agar becomes dry, the bacteria 

 usually die. If, however, the tube be sealed with parafin or 

 sealing wax, it can be kept for months, in many cases for years, 

 without dying. After purifying the cultures, carefully label, 

 and reserve them for future use. 



*No. 15. Microscopic Study. Prepare one or both of the fol- 

 lowing staining solutions: 



Methylene Blue 



Saturated alcoholic solution of Methylene Blue 15 c.c. 

 Potassium Hydrate (i: 10,000)* . . . . f 50 c.c. 



Fuchsin Solution 



Saturated alcoholic solution of Fuchsin ... 5 c.c. 

 5% solution of carbolic acid 45 c.c. 



Place an ordinary cover-glass in a special pair of forceps 

 (Fig. 80) and in the center place a very small drop of sterilized 



FIG. 8O FORCEPS FOR HOLDING COVER-GLASSES WHILE STAINING 



or boiled water. With a platinum needle remove a very small 

 quantity of the bacteria growth from the surface of an agar 

 tube of No. 14 and place in the water drop. Stir this drop with 

 the platinum wire, to distribute the bacteria, and spread as 

 widely as possible over the cover-glass. Allow to stand in the 

 air until dry, and then pass the cover-glass through a gas flame 

 quickly three times. The purpose of this is to fasten or fix the 

 bacteria firmly to the glass so that they will not wash away. 

 It is necessary to avoid using too much heat, for over-heated 



1 To make this solution add 1 c.c. of a 10 per cent. KOH solution to 99 c.c. 

 of water, and then add 5 c.c. of this to 45 c.c. of water. 



