FERMENTATION ORGANISMS 118 



Exercise 156. Obtaining Mold Cultures from Spores in the Air 



1. Put some slices of bread on a plate and steam them for 

 ten minutes in the Arnold sterilizer. 



2. Remove and place the plate on a laboratory table for 

 fifteen minutes, then cover with a bell jar. 



3. Under another bell jar place slices of lemon or pieces of 

 cheese. 



4. Examine the cultures day by day until they show spores. 

 The material may be used for study, or pure cultures may be 

 prepared by using the isolation methods described in Exercise 63. 



Exercise 157. Culture of Molds on Liquid Media 



Mold fungi are usually capable of culture upon the surface of 

 liquid media. The mycelium of Aspergillus or Penicillium forms 

 a disk which floats upon the surface of the liquid. Spores will 

 develop upon the upper surface of the disk of mycelium. 



1. Prepare 100 cc. of the synthetic solution described in 

 Exercise 54 ; divide it between two Erlenmeyer flasks of 200 cc. 

 capacity. 



2. Make a series of other solutions in which substitutions are 

 so made that one essential element is lacking in turn from some 

 solution in the set. 



3. Sterilize the flasks in the Arnold sterilizer. Inoculate with 

 Aspergillus or Penicillium and make records of the amount of 

 mycelium and spore formation in each. 



Exercise 158. The Stimulating Action of Weak Poisons 



The physiological action of small amounts of poison may be 

 well demonstrated by the culture of fungi on liquid media. In 

 the weak dilutions there will be stimulation, while at higher 

 concentration there is toxic action. 



1. Prepare a liter of the synthetic solution as in the fore- 

 going exercise. 



2. Measure off 50 cc. portions which can be put into 200-cc. 

 flasks. 



