The Laboratory 73 



bing. Do not pour exhausted solution down the 

 sink! It can be emptied in some waste place 

 where it will do no serious damage. 



Nutrients will generally be made up in 4-liter, 

 10-liter, or 20-liter serum bottles (see later). A 

 supply of graduates of various sizes, 125, 250, 

 500, and 1000 ml. Erlenmeyer flasks, 500, 1000, and 

 3000 ml. balloon flasks, test tubes, pipettes, etc., 

 will be required for the preparation of different 

 nutrients and should be kept in the media room. 

 Both absorbent and non-absorbent cotton, a good 

 grade of cheesecloth, heavy paper for wrapping 

 glassware for dry-sterilization, cord, stones for 

 sharpening instruments, etc., should also be pro- 

 vided. 



Cotton plugs for flasks should be of non-ab- 

 sorbent cotton and should be wrapped in cheese- 

 cloth. This reduces the danger of plugs sticking 

 to the mouths of the flasks, prevents loose fibers 

 from falling into the flasks, and helps to preserve 

 the form of the plugs. Plugs prepared in this 

 way can be used repeatedly. It has been found 

 best to cover each plugged flask with an inverted 

 50 ml. beaker to keep out dust and water of con- 

 densation, else molds are likely to grow in the 

 plugs and ultimately penetrate to the nutrient 

 (Figs. 29-31). (See Tukey, 1934,57). Metal trays 

 13" X 21" X 3^" (Fig. 31) are of the proper dimen- 



