NOTE BY THE TRANSLATOR. 



THIS book is in many respects a companion volume to 

 " Ferments and their Actions," by the same author. As 

 in that case, I have made numerous additions to the text, 

 so as to include the more important facts that have been 

 made known since the appearance of the German Edition, 

 and the selection from the voluminous mass of new 

 matter has been made by Dr. Oppenheimer himself. 



C. A. M. 

 GRAY'S INN, 

 LONDON, W.C., June, 1906. 



