APPRECIATION 



Difco Laboratories desires hereby to acknowl- 

 edge its indebtedness to the many microbiolo- 

 gists from whom it has so often sought advice 

 and whose cooperation and assistance it has so 

 frequently received in the development, im- 

 provement and standardization of these prod- 

 ucts. 



Acknowledgment is also made of the use of 

 published papers and textbooks as a source of 

 much of the material in this book. 



