52 



A MANUAL OF THE ASPERGILLI 



midity, are favorable as at Baarn, Holland, refrigeration may be dispensed 

 with, but watchfulness against invasion by mites becomes more important. 

 Additional slants should be prepared for cultures which are frequently used. 

 Agar slant cultures are convenient for use, easily examined and com- 

 pared, and easily replaced (fig. 13 A). They are, however, easily contami- 

 nated when handled carelessly. Uneven drying subjects the culture to 



Fig. 13. Methods of maintaining stock cultures as discussed in the text. A, 

 Cultures growing on agar slants. B, Cultures preserved in lyophile form; note the 

 compact, chalky pellets formed by the dried serum in which the spores are suspended. 

 C, Cultures preserved in dry soil. 



extremes of contrast in concentration of media and metabolic end products, 

 between the thin edge of the slant and the heavier mass in the bottom of the 

 tube. Variations (apparent or real) often appear in the stored cultures 

 and these may be propagated in subsequent transfers. As a safeguard, 

 stock cultures should be grown in petri dishes after several transfers in tubes, 

 thus making possible more complete examination to maintain purity and 

 typical morphology. 



