CONVENIENT METHODS FOR DEMONSTRATING 



THE BIOCHEMICAL ACTIVITY OF MICRO- 



ORGANISMS, WITH SPECIAL REFER- 



ENCE TO THE PRODUCTION 



AND ACTIVITY OF 



ENZYMES 



C. H. CRABILL and H. S. REEDi 



(WITH PL ATE l) 



Introduction. A large amount of work has been done on the 

 biochemistry of microorganisms and many reliable tests f or demon- 

 strating these activities have been evolved. Some of the tests are 

 not well adapted for ocular demonstration to classes, however, 

 because of their transitoriness or for other reasons. We have 

 thought it worth while to describe in the following paragraphs a 

 few methods, for making semi-permanent demonstrations of these 

 activities, which seem adapted to the needs of class room or labo- 

 ratory instruction. Some of the methods given here are adapted 

 from those of other investigators ; other methods are original with 

 the present writers. 



The methods are designed to show the presence and action of 

 products of cellular activity upon appropriate substances incor- 

 porated in thin layers of agar in Petri dishes. Agar seems to serve 

 very well for this purpose, since it is not difficult to prepare a clear 

 Solution, and most solutes diffuse readily through the gel which it 

 f orms. When solid zymolytes are used they are suspended in the 

 agar. In order to procure uniform distribution of these solids 

 through the medium, the plates are poured directly from the flask 

 in which the medium is cooked and sterilized. By frequent shak- 

 ing between pourings, settling of the solids is prevented. With 

 this procedure, tubing of the medium is entirely unnecessary, if not 

 detrimental to the best results. Stain reduction cannot be well 



1 Paper No. 29 from the Laboratories of Plant Pathology and Bacteriology,. 

 Virginia Agricultural Experiment Station, Blacksburg. 



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