Micro-organisms of Maple Sap 525 



METHODS OP WORK 



Throughout the studies great care was exercised to secure 

 uniformity of methods so that the results with the several strains 

 might be comparable. In general the methods recommended in 



"Standard Methods of Water Analysis*' (1905) and in Smith's 

 "Bacteria in Relation to Plant Diseases" (27) have been followed, 

 but in certain respects it has been deemed wise to introduce varia- 

 tions. The most important of these is the substitution of 

 "Liebig-'s Extract of Meat" for beef infusion. Media prepared 

 with meat extract has been used in this laboratory for several 

 years and has always given satisfaction. It is believed that media 

 prepared in this way is more uniform in composition than that 

 from infusion and it also possesses the very decided advantage 

 of being- free from muscle sugar. Actively fermenting strains of 

 B. coli develop in it without producing- visible gas. The objec- 

 tions usually advanced against meat extract that it frequently 

 contains resistant spores, that it may have been treated with pre- 

 servatives, or that it may contain injurious by-products of bacterial 

 development, have not seemed to be well founded. In our ex- 

 perience there is never more difficulty in sterilizing meat extract 

 than in sterilizing- beef infusion and we have never been able to 

 discover indications of preservatives or injurious decomposition 

 products, the most sensitive organisms developing as readily upon 

 one type of medium as upon the other. When cultures are to be 

 employed in studying gas evolution or acid formation, muscle 

 sugar introduces a complication. Jt is the general custom to 

 remove this by cultivating an active fermenter in it for a few- 

 hours. This is objectionable and is certain to introduce decom- 

 position products to such an extent as to render the media quite 

 unfit for the development of certain sensitive species. There is 

 great need of synthetic substitutes for the beef media composed of 

 synthesized chemicals, but until they are developed we believe the 

 employment of a standard brand of meat extract has points of 

 advantag-e over infusion. 



