EXERCISE 81 

 DETECTION OF MOLDS IN AIR AND IN OTHER PLACES 



Materials. Sterilized petri dishes ; one of the common dessert 

 gelatins which are sold under various trade names, or agar culture 

 medium. 



Directions for work. Tests for the presence of mold spores 

 in the air and in various media may be made in a manner 

 similar to that described for bacteria (Exercise 76). In fact, it 

 is probable that many mold colonies were found among the 

 bacterial colonies. Very satisfactory substitutes for agar are 

 the various sorts of gelatin sold for household use. If these 

 are purchased in sealed packages, they will be practically sterile 

 and will need no further sterilization than the boiling needed 

 to dissolve them. Pour in shallow dishes and allow to cool in 

 the usual way, or some of the material may be placed in sterile 

 test tubes and plugged with cotton. 



Expose the petri dishes with the culture medium in situa- 

 tions similar to those suggested for the bacterial cultures 

 (Exercise 76), or inoculate them directly from other cultures 

 of mold. 



Keep several petri dishes or test tubes uninoculated, as a 

 check upon the sterile character of the medium. Set all the 

 dishes in a warm place, where they may be examined from 

 time to time without disturbing them. From day to day note 

 carefully the first appearance of the colonies and the changes 

 that take place. The cultures will afford the materials for use 

 in the following exercises. 



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