LABORATORY AND TEACHING METHODS 



597 



Glycerin Potato Broth. — i. Take i kilo of potatoes, wash thoroughly in H2O, 

 peel and grate finely on a bread grater. 



2. Weigh the potato gratings, place them in a 2-liter flask, and add distilled 

 water in the proportion of i c.c. for every gram weight of potato. Allow the flask 

 to stand in the ice chest for twelve hours. 



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Fig. 210. — Knife punch designed to 

 cut cylinder of potatoes and other vegeta- 

 bles for insertion as slant cylinders in 

 test-tubes as culture media. 



Fig. 21 r. — Culture tube with bulb 

 to hold glycerine and water below 

 slant of vegetable. 



3. Strain the mixture through cheese cloth and filter into a graduated cylinder. 

 Note the amount of the filtrate. 



4. Place the filtrate in a flask, add an equal quantity of distilled water, and 

 heat in a steam sterilizer for an hour. 



5. .Vdd glycerin, 4 per cent., mix thoroughly and again filter. 



6. Tube°and sterilize in the steamer at ioo°C. for twenty minutes on each of 

 three consecutive days. 



