NUTRIENT MEDIA AND METHODS OF CULTIVATION. 



103 



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

 hour a day for three successive days. 



If the gelatine shows any turbidity after these processes it must 



Fig. 32. — Method of making a Folded Filter. 



be poured back from the test-tubes into a flask, boiled up for ten 

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

 described must be repeated. 



Fig. 



-Steam Stebilisee. 



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 boils at 90° C, and 



