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. 
t= a 
tet « ue 
ie, 
ret 
i" rps 
b 
Fig. 31.* 
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 /tmus-lactose agar, 
which is made out of ordinary 
nutrient agar by adding 1 per 
cent milk-sugar and enough 
pure litmus water to give a pur- 
ple-red color. Glycerin-agar, 
maltose-agar, etc., may be made 
up with any amount of the sub- 
stance desired, generally 1 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 2G. ;.2:.2,,-110~-C. 
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 foran hour or more 
z. é., 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 
*Fic, 31.—Red sea-weeds from which agar-agar is manufactured. a, Gelidium corneum Lam., 
one-third natural size; b, Gelidium subcostatum Lam., one-half natural size. Froma colored Jap- 
2 | anese chart showing “The principal aquatic plants of Japan,” supposed to be an official publication. 
t Original in the fibrary of the United States Fish Commission. 
