'6 10 LABORATORY EXERCISES 



of Cellulose by Bacteria and Fungi. Bull. 266, Bureau of Plant Industry, 1913: 28). 

 — Pare, steam and mash a quantity of potatoes. To 100 grams of mashed potato 

 add 800 c.c. of tap water ar.d steam for one-half hour; filter through cotton. 



Potato solution, c.c 500 



Agar, grrims 15 



Nutrient solu tion, c.c 500 



Potato Agar (AnCither formula). — Put clean pared potatoes through a meat 

 gB-inder. To 1000 gn ims'of the potato pulp add an equal quantity of distilled water. 

 Stir thoroughly aJid let stand in an ice box for an hour, with occasional stirring. 

 Strain through gauz€ of medium mesh. Make up to three times the weight of the 

 original pulp with di stilled water. Strain for one hour, filter through cotton and 

 paper and make up to 3000 c.c. with distilled water. Add i^i, per cent, of agar 

 flour, steam for one hour, filter through cotton and paper, tube and autoclave for 

 fifteen minutes at 1 1 s^C. As this potato agar varies widely in acidity, to reduce this 

 variation a large cjuan tity of potato juice made from a uniform lot of Burbank po- 

 tatoes is used. This if , placed in looo-c.c. flasks tightly plugged and kept in a refrig- 

 erator. The juice is "then made up in agar tubes as needed. It was found that this 

 agar varied less than i per cent, in acidity, changing from -[-7 to -|-6 during five 

 months. 



LESSON 16 



Starch Agar— -TfefSjoo c.c. of boiling water add 10 grams of potato starch sus- 

 pended in a little eoitfi water.. Concentrate by boiling to 500 c.c. This breaks up 

 the starch grains endJ it should give a nearly transparent starch solution. 



Starch solu ifiiiam, c.c Soo 



Nutrient S( Jtetion (same as for cellulose agar), c.c 500 



Agar, gran is... 10 



Cellulose Agar (Ai "^cBeth and Scales: Bull. 266, Bureau of Plant Industry, 

 p. 27). — Prepare a^ Mt< ^r of dilute ammonium hydroxide solution by adding 3 parts 

 of water to 10 parts o; f ammonium hydroxide, sp. gr. 0.90. Add a slight excess of 

 copper carbonate ands. hake, allow to stand over night and then siphon off the super- 

 natant solution. AcM 10 grams of unwashed sheet filter paper and shake occasion- 

 ally until the paper isi; 'ssolved. Dilute to 10 liters and add slowly a i to 5 solution 

 of HCl, with vigorous , shaking until the precipitation of the cellulose is complete. 

 Dilute to 20 liters, fjilib? w the cellulose to settle and decant the supernatant liquid. 

 Wash by repeated clha iges of water, adding HCl each time until the copper color 

 disappears; then wa^ with water alone until the solution is free from chlorine. 

 Allow it to settle severnil days and decant off as much of the clear solution as possible. 

 If the percentage of: fflt llulose is still too low, a portion of the solution is centri- 

 fugalized to bring i-^ ifc ellulose content up to i per cent. 



