NUTRIENT MEDIA AND METHODS OF CL'LTIVATION. 



103 



may be transferred to the test-tube water-bath, and heated for an 

 hour a day for tliree successive days. 



If the gelatine shows any turbidity after these processes it must 



Fio. 32. — Metholi of .m.\king a Folded Filteu. 



be poui-ed back from the test-tubes into a flask, bailed up for ten 

 minutes, and iiltered once more, and the processes of sterilisation just 

 described must be repeated. 



Fig. 33.— ISteam Stehilisei;. 



Nutrient Agar-agar. — Agar-agar is a substance prepared 

 from seaweed which grows on the coasts of Japan and India, 

 and is supplied in long crinkled strips. It VjoiLs at 90° C, and 



