vi PREFACE 



has unquestionably been very great. At the same 

 time it cannot be doubted that some of the deduc- 

 tions from the theory have led, here and there, 

 to strained conceptions which apparently violate 

 established biological facts. While presenting 

 Ehrlich's views at length, therefore, the author 

 has endeavored to bring out clearly just why and 

 wherein certain other investigators differ. The aim 

 of the book has been to present a broad, clear outline 

 of the main facts and theories concerning infection 

 and immunity, and while this may perhaps have 

 led to the omission of some really excellent studies, 

 it was felt best not to confuse the beginner with a 

 mass of apparently contradictory observations. 



CHARLES BOLDUAN. 



NEW YORK, April, 1911. 



