PREPARATION OF NUTRIENT AGAR. 



33 



For a full account of Japanese methods of making agar-a.^ar consult a ])a])er 



entitled "The Seaweed Industries of Japan," by Dr. 

 of the United States Bureau of Fisheries for 1904. 



h 

 Fig. 31.* 



Hugh M. Smitli, in the Ilulletin 



In addition to beel Ijouillon, 

 or in place (jf it, various sub- 

 stances, organic and inorganic, 

 may be added to the agar with 

 advantage. The writer makes 

 nuich use of Utimts-lactosc a^ar^ 

 wliich is UKide out of ordinary 

 nutrient agar 1)}- adding i per 

 cent milk-sugar and enough 

 pure litmus water to gi\'e a pur- 

 ple-red color. C/ycvriit-a'^ar, 

 ii/altosc-agar, etc., ma\- be made 

 up with an)' amomrt of tlie sub- 

 stance desired, general!)' i or 2 

 per cent. 



Former!)' it was difhcult to 

 filter agar perfectly clear and it 

 was therefore used less than 

 gelatin, l)ut in recent )'ears it 

 has been discovered that this 

 difficult)' ma)' be overcome if 

 the agar is first brought into 

 complete solution b)- prolonged 

 boiling or 1jy a short boiling at 

 a temperature somewhat above 

 100° C, c. o-.^ 110° C. 



The writer formerly obtained 

 filtered clear agar h)' soaking 

 the snipped agar in 5 ]:)er cent 

 acetic-acid ^\'ater for some hours, 

 after which a thin clotli \\as tied 

 over the nu:)Utli of tJie l)eaker 

 securel)', and tap water allowed 

 to run into it for an hour or more 

 /. c, until all trace of acid was 

 removed. The softened agar 

 was then put into the bouillon, 

 boiled for two hours, and fmally 

 filtered through S. & S. filter 



*FiG. 31. — Red sea-weeds from wliich agar-agar is niaimfactured. a, Cclidiiim coiiu-niii Lam,, 

 one-third natural size; b, GcUdiiiin siibcostatum Lam., one-half natural size. From a colored Jap- 

 anese chart .s'hovving " The principal aquatic plants of Japan," supposed to be an official publication. 

 Original in ifhe library of the United States Fish Commission. 



