PREFACE TO THE FIRST EDITION 



between hypotheses and facts. For these reasons I 

 have limited myself to making mention of those 

 works which either are closely connected with my 

 own researches, or else will be of special service to 

 the reader, in that the full lists of references they con- 

 tain will be a guide to further study in this field of 

 research. This limitation alone has enabled me to 

 present a picture which, I hope, is quite clear of 

 the development of my own investigations, and to 

 show ho\v I arrived at the doctrine of the active part 

 played by ferments in connection with disharmonious 

 substances. 



The comprehensive survey, which I now present, 

 has resulted from the fact that many problems have 

 been so far advanced, recently, by means of experi- 

 mental work, that it seemed advisable to take stock of 

 the observations that lie stored in numerous pub- 

 lications. And, on the other hand, I find that the 

 further study of particular problems can be carried 

 on only in institutions supplying means and 

 apparatus which I cannot command. One man 

 by himself is able in certain problems to reach 

 only a certain point. He takes over, as it were, 

 an edifice which has been built up to a certain 

 height from all possible sides. He tests the 

 scaffolding the existing working theories to see 

 whether it will last any longer, or whether it must be 

 replaced ; and, more important than that, decides 



