viii PREFACE 



incorporated in the book. In order to make it easier for the 

 reader to visuahze the experiments a large number of drawings 

 from nature are introduced in the text, for which the writer is 

 indebted to Miss M. Hedge of the Ilkistration Division of the 



Institute. 



Jacques Loeb. 



The Rockefeller Institute 



OF Medical Research, 



New York. 



January, 1924. 



