Acknowledgments 



This book was written in a provisional form in 1930 and in the follow- 

 ing years; however, it was not yet quite finished by 1937. In 1937 a 

 grant was received from the Josiah Macy Jr. Foundation for its com- 

 pletion ; this, as well as a revision, was accomplished between the latter date 

 and the present time. The writer wishes to express his appreciation to the 

 Josiah Macy Jr. Foundation for the assistance thus given. 



To the International Cancer Foundation the author is indebted for grants 

 which enabled him to undertake additional experiments concerning a com- 

 parison between the individuality differentials of normal and cancerous tissues. 

 In this volume the results obtained have been incorporated. 



Sincere appreciation is also due to the numerous collaborators who helped 

 to advance this field of research during the many years in which these in- 

 vestigations were carried out. Reference is made in the text to their contribu- 

 tions. The co-operation of Dr. Helen Dean King and Dr. Sewall Wright and 

 subsequently also of others was of very great help in making possible the 

 transplantation of tissues in closely inbred strains of rats and guinea pigs. 

 Later, there were added to these experiments those on closely inbred strains 

 of mice which were received from the New York State Institute for the Study 

 of Malignant Disease, from the Roscoe B. Jackson Laboratory, Bar Harbor, 

 and from other laboratories. 



The aid given by the wife of the author, Georgiana Sands Loeb, in the re- 

 vision of this manuscript, and in other ways through many years, was of the 

 greatest value and to her this book is gratefully dedicated. 



To Mr. Charles C Thomas, I wish to express my warm appreciation of the 

 great interest and helpfulness he has manifested in the publication of this book. 



IX 



