CHAPTER XII. 

 ACTIVE IMMUNIZATION. 



IF now we pass on to a discussion of the different defensive factors 

 of the animal body from the standpoint of prophylactic and curative 

 therapeutics the question naturally arises, To what extent have we 

 the power to influence this mechanism artificially? In view of the 

 fact that we have scarcely passed farther than the threshold of the 

 study of immunology, using the term in its widest sense, it is natural 

 that our attempts to utilize the principles with which we have thus 

 far become acquainted should have been relatively crude, and that 

 the results in many instances have not led to a satisfactory end. 

 An enormous amount of work still remains to be done, but even so 

 we have every reason to be proud of what has already been achieved, 

 and to believe that more yet will be accomplished in the future. 



We have seen that even under normal conditions the body has at 

 its disposal defensive forces which are most important, and which 

 in many instances are quite sufficient to prevent a general infection, 

 even though the local barriers have fallen. The battle here is, no 

 doubt, frequently won before specific antibody formation our 

 second line of defence has even begun. For many centuries 

 physicians have recognized the existence of so-called predisposing 

 causes to disease and their influence upon the course of the individual 

 case. I would recall the effect of depressing influences, such as grief 

 and worry, fatigue and hunger, in increasing the predisposition to a 

 great many infectious diseases. 



Quite in accord with clinical observation are the results of the 

 animal experiment. Charrin and Roger thus succeeded in infecting 

 rats with anthrax after they had been greatly fatigued by being 

 made to run in a tread-mill, while under normal conditions the 

 animals are quite resistant. Other observers could break the natural 

 immunity of dogs, chickens, and pigeons to the same organism by 

 the withdrawal of drinking water; in pigeons the same result can be 

 obtained by fasting. Quite well known further, both clinically 



