PREFACE 



INFECTIOUS disease, biologically considered, is the reaction which 

 takes place between invading micro-organisms and their products, on 

 the one hand, and the cells and fluids of the animal's body on the 

 other. The disease is the product of two variable factors, each of 

 them to a certain extent amenable to analysis, and it is self-evident 

 that no true understanding of this branch of medicine is possible 

 without a knowledge of the biological principles which laboratory 

 study has revealed. 



For the purpose of helping to render such knowledge easily ac- 

 cessible this book was written. While it is hoped that it may prove 

 useful to the practitioner and laboratory worker, it is intended pri- 

 marily for the undergraduate medical student. To many it will 

 seem that the subject in general and our method of treatment espe- 

 cially are too technical and difficult for this purpose. Our own ex- 

 perience contradicts this. During the past three years the writer has 

 had the opportunity to deliver lectures and to give laboratory courses 

 on this subject to medical students of 2d, 3d, and 4-th-year classes at 

 the Stanford and Columbia Universities. It has been a pleasant 

 experience to find the medical student eager for the opportunity to 

 obtain this knowledge and, under the present increased require- 

 ments for preliminary training at our best schools, fully capable of 

 assimilating it. It is not a good plan to attempt too extensively to 

 simplify material that, in its close analysis, presents complex phe- 

 nomena and intricate reasoning. For this reason no attempt has 

 been made to write an A B C of immunity as a quick road to com- 

 prehension. No true insight into any branch of medicine or, for that 

 matter, into any other science, can be attained without a certain 

 amount of labor; however the concepts of this subject are, indeed, 

 relatively simple after the first principles have been mastered, and 

 the writer has attempted, therefore, at the risk of seeming pedantic 

 in places, to treat the subject critically, separating strictly those 

 data which may be accepted as fact from those in which legitimate 

 differences of opinion prevail. 



As far as was feasible every chapter has been written as a sepa- 

 rate unit. This has necessitated occasional repetition, but, it is 

 hoped, will add considerably to clearness of presentation in each indi- 

 vidual subject. Theories have been discussed with as little prejudice 

 as the possession of a personal opinion in many cases has permitted. 



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