PREPARATION OF NUTRIENT AGAR. 



33 



For a full account of Japanese methods of making agar-agar consult a paper 

 entitled "The Seaweed Industries of Japan," by Dr. Hugh M. Smith, in the Bulletin 

 of the United States Bureau of Fisheries for 1904. 



In addition to beef bouillon, 

 or in place of it, various sub- 

 stances, organic and inorganic, 

 may be added to^the agar with 

 advantage. The writer makes 

 much use of litmus-lactose agar, 

 which is made out of ordinary 

 nutrient agar by adding i per 

 cent milk-sugar and enough 

 pure litmus water to give a pur- 

 ple-red color. Glycerin-agar, 

 waltose-agar, etc., may be made 

 up with any amount of the sub- 

 stance desired, generally i or 2 

 per cent. 



Formerly it was difficult to 

 filter agar perfectly clear and it 

 was therefore used less than 

 gelatin, but in recent years it 

 has been discovered that this 

 difficulty may be overcome if 

 the agar is first brought into 

 complete solution by prolonged 

 boiling or by a short boiling at 

 a temperature somewhat above 

 100 C, e.g., uoC. 



The writer formerly obtained 

 filtered clear agar by soaking 

 the snipped agar in 5 per cent 

 acetic-acid water for some hours, 

 after which a thin cloth was tied 

 over the mouth of the beaker 

 securely, and tap water allowed 

 to run into it for an hour or more 

 /'. e., until all trace of acid was 

 removed. The softened agar 

 was then put into the bouillon, 

 boiled for two hours, and finally 

 filtered through S. & S. filter 



6 

 Fig. 3 1* 



*Fic. 31. Red sea-weeds from which agar-agar is manufactured, a, Gelidium corncum Lam., 

 one-third natural size; b, Gelidium subcostatum Lam., one-half natural size. From a colored Jap- 

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

 Original in the library of the United States Fish Commission. 



