by laying before you some of the more important points con- 

 cerning the part played by these organisms when present in 

 the bodies of hving animals, in other words concerning their 

 relationship to certain diseases. I must ask your pardon if 

 I fail to make the subject as clear as could be wished ; for 

 our knowledge is at present only fragmentary, and the inves- 

 tigation of the question is beset with difficulties, not only in 

 conducting experiments, but also in reasoning correctly from 

 their results. 



To the outsider it may possibly appear that the theory 

 of the production of certain ailments, and their communication 

 from one individual to another by means of living organisms 

 is altogether a new departure in the study of disease. It is 

 not so ; on the contrary the enquiries of scientific observers 

 have gone on step by step until the minds of Pathologists 

 were in a condition at once to accept such a discovery, as 

 the completion of what may be considered to be a true 

 scientific induction. I hope I shall not be wasting your 

 time if I occupy a few moments in explaining what I mean. 

 Without giving a regular history of the subject, I may 

 say that we have probably come to our present state of know- 

 ledge somewhat in the following way : — If we examine the 

 condition of a sick man, we find that the physiological func- 

 tions impelled by some morbific influence, have lost their 

 natural equilibrium. On the medical side we see, perhaps, 

 fever, headache, and the like ; on the surgical side, possibly 

 pain, swelling, redness, and the other conditions of inflam- 

 mation. The old professors of the healing art imbued with 

 the teachings of the Ancient Schools of Philosophy speculated 

 upon the nature of these Phenomena, and invented various 

 theories more or less absurd to account for them. Theories 

 which bore the stamp much more of the library than of the 

 bedside or the dissecting room. 



After a time it was noticed that in certain cases not only 

 were these general disturbances present, but there were also 

 developed some special symptoms which were peculiar to the 

 disease in question, and that these symptoms were invariably 



