INTRODUCTION 3 



necessarily give rise to disease, for many are harm- 

 less, although they may be present in the blood and 

 tissues. Not even in the case of an infectious disease, 

 where a certain microbe is present, can one say that 

 it is the cause of that disease. Not until Koch's 

 canons are fulfilled, is the experimenter justified in 

 saying that any particular microbe is pathogenic or 

 disease-producing. 



From what has been said, it will be seen that 

 bacteriology, as applied to disease, is dependent 

 upon observation of, and experiments upon, living 

 matter. Among phenomena of so complex a char- 

 acter as infectious diseases, simple observation goes 

 but a very little way, and our knowledge of all the 

 most important truths of bacteriology, as applied to 

 these diseases, has been obtained by experimentation 

 upon living animals. 



Vivisection is necessary for a proper interpreta- 

 tion of the phenomena. But ' every now and again 

 a loud outcry is raised against this method, partly 

 from ignorance and partly from prejudice. Many 

 probably most of the opponents of experiments on 

 animals are good, honest, kind-hearted people, who 

 mean well, but either forget that man has rights 

 against animals as well as animals against man, or 

 are misled by the false statements of the other class. 

 These are persons who, blinded by prejudice, regard 

 human life and human suffering as of small import- 

 ance compared with those of animals, who deny that 

 a man is better than many sparrows, and who, to the 

 question that was put of old, " How much, then, is 

 a man better than a sheep?" would return the reply, 



