6o8 



LABORATORY EXERCISES 



LESSON 14 



General Directions for Making Plant A gars. — Plant agars of various kinds may 

 be made by substituting the desired decoction (made as directed later) for the 

 bouillon and each looo c.c. of agar should contain the soluble nutrients from 50 

 grams of dry weight of the plant structure used. 



Decoctions (F. D. Heald) are made by adding 1000 c.c. of cold distilled water to 

 50 grams dry weight of the substance. Heat in a steam sterilizer and boil for 

 fifteen minutes. The following data are applicable in this connection. 



Table of Dry Contents 



Potato 



Sugar beet 

 Carrot 



Celery 



Corn meal. 



Water 

 content, 

 per cent. 



Dry 

 substance, 

 per cent. 



Approximate weight 



giving so grams of dry 



substance, grams 



Corn Meal Agar. — This nutrient medium is made by taking 300 grams of corn 

 meal and adding 1000 c.c. of distilled water. Heat it in a cooker over a gas burner 

 and boil for fifteen minutes. The decoction is then made up with agar being used in 

 place of bouillon. Clinton (Conn. E.xper. Sta. Rep. 1907-08: 898) gives these 

 directions for making corn meal juice agar. With a 50 + 10 + 500 formula; that is, 

 50 grams of dried corn meal (= 300 grams of wet corn meal), 10 grams agar-agar 

 and SCO c.c. of water. The corn meal is made into a decoction by using not over 

 500 c.c. of water strained through fine cloth, the agar-agar is added, heated long 

 enough to mi.x agar-agar and filtered. 



Corn Meal Agar {Another Formula). — To 50 grams of corn meal add 1 liter of 

 water. Keep in a water bath for one hour at a temperature of 58°C., never over 60°. 

 Filter through paper, add lY^ per cent, of agar flour, steam for 1^2 hours, filter and 

 tube. Autoclave for fifteen minutes at ii5°C. Corn meal agar made by the above 

 formula generally tests +3. 



Lima Bean Juice Agar (Clinton: Conn. Exper. Sta. Rep. 1907-08: 898). — Use 

 a 50 + 10 + 500 formula; that is, 50 grams of dried ground lima beans, 10 grams of 

 agar-agar and 500 c.c. of water. The beans are ground as fine as possible with a 

 fruit grinder, and then 50 grams are soaked one-half hour in tepid water (use as 

 much water as necessary, but of course not to exceed 500 c.c. finally) and then 

 simmer slightly for another half hour. Strain off the liquid through a fine wire 

 strainer, add agar-agar (better dissolve in a small amount of water) and add water 

 necessary to make 500 c.c. of medium; heat long enough to thoroughly mix the agar- 

 agar and strain through fine cloth into test-tubes. 



