Xll PREFACE 



nificance of the reaction. This he can do only by equipping himself 

 with the knowledge of the fundamental factors of immunity, or he will 

 be forced into the position of a passive transmitter of ideas entirely be- 

 yond his own knowledge. 



2. An effort has been made to include data of both practical and 

 theoretic importance, and in some instances tests are described that are 

 more of theoretic than of practical import, especially in research work. 



It is obviously impossible, in a single volume, to include the very 

 large number of tests and modifications that have been advocated from 

 time to time, and, as a matter of course, most attention has been given 

 those methods that have been shown to be of practical value or that 

 give promise of becoming so. So far as possible original methods are 

 given, these being, in the larger proportion, more or less important modi- 

 fications devised as the result of my own experience in hospital and teach- 

 ing laboratories. 



The technic of the various tests and reactions is described in great 

 detail, thus tending the better to secure accuracy, simplicity, and definite- 

 ness, and to serve as an opening wedge to those about to enter this 

 special field. 



3. The value of the experimental method in the teaching of certain 

 branches of medicine is now well recognized. In no department, how- 

 ever, is this method of greater value than in the study of infection and 

 immunity. A working knowledge of these subjects is so valuable in the 

 practice of medicine and surgery that the student should be well versed 

 in at least their primary principles and practical applications in the 

 prophylaxis, diagnosis, and treatment of diseas 



The laboratory course given in Part V is based upon the courses 

 given by me in the Laboratory of Experimental Pathology at the Uni- 

 versity of Pennsylvania, and in the laboratories of the Philadelphia 

 Polyclinic and College for Graduates in Medicine. In including them 

 in this volume I am carrying out my original plan, for in many of the 

 experiments the exact technic of a given test is described, making a sepa- 

 rate book devoted to this part of the subject unnecessary. Future ex- 

 perience may, however, show the necessity of having this portion of the 

 book form a separate laboratory manual. I shall appreciate the opin- 

 ions of educators who may have occasion to consult the course herein 

 outlined. 



Since the larger portion of our knowledge of infection and immunity 

 has been gained from studies upon the lower animals, it is not strange 

 that these were early and directly benefited by a practical application 



