vi PREFACE 



a great deal of scientific interest, namely, haemoly- 

 sins, cy to toxins, and precipitins. To this was 

 added, in subsequent editions, a discussion of anti- 

 toxins, agglutinins, and opsonins. All these topics 

 were naturally embraced under the title "Immune 

 Sera." In the present (fourth) edition, while the 

 old title has been retained, the scope of the sub- 

 ject matter has been greatly extended, so that now 

 there is presented an exposition of the main facts 

 of infection and immunity. 



It is but natural that any discussion of the 

 immunity reactions should center about the ingen- 

 ious side-chain theory of Ehrlich, which has domi- 

 nated the work in this field. Its heuristic value 

 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. 



