AGAR 37 



just previously washed with 1/2 liter boiling water. Pass 

 the filtrate through the same paper until it is bright and 

 clear. 



13. Fill thirty sterile test tubes, using approximately 

 8 c.c. of medium for each tube. Divide the remainder into 

 two equal portions and place in sterile 1/2 liter Erlenmeyer 

 flasks. 



14. Heat in flowing steam twenty minutes on three 

 successive days. 



15. Cool the gelatin in a running-water bath, immediately 

 after each heating. Care must be taken to heat the gelatin 

 as little as possible, since part of the solidifying power of 

 gelatin is lost with each application of heat. 



16. To sterilize a large flask of nutrient gelatin, heat 

 for twenty minutes on four days in succession. 



AGAR 



Agar or agar-agar (from a Malay word meaning " vege- 

 table "), the substance which is used in preparing one kind 

 of solid culture medium for bacteriological work, is a pro- 

 duct prepared from various seaweeds found near the Indian 

 Ocean and in Chinese and Japanese waters. This type of 

 seaweed has several common names, as Ceylon or .Jaffna 

 moss, Bengal isinglass, etc. Various species are used for 

 food and the trade is considerable. 



Payen, a French chemist -(about 1859), obtained the 

 agar jelly from the seaweed, Gelidium corneum, in the fol- 

 lowing manner : The seaweed was allowed to stand for some 

 time in a cold dilute solution of hydrochloric acid; the acid 

 was removed by rinsing several times with water, then the 

 seaweed was placed in a cold dilute solution of ammonia; 

 next the ammonia was removed by repeated rinsing with 

 cold water. During this process, the seaweed lost 53% 

 of its weight in mineral salts, coloring matter, and organic 

 constituents. The remaining portion was boiled in water, 



