THE GERM THEORY OF CARIES. 153 



while the general fluids of the mouth may be neutral, or 

 even alkaline. 



The manner of the production of this acid has been a 

 subject of much inquiry. All, I believe, admit that it must 

 come in some way through fermentation or decomposition ; 

 at any rate, through a rernoleculization of the substances 

 lodged about the teeth. This leads directly to the discussion 

 of the much vexed question of the fermentations and de- 

 compositions, and the relations of the life force thereto. The 

 research of the last few years leaves but little doubt on this 

 point. These processes are the result of the activity of living 

 organisms. The teachings of Liebig on this subject may now 

 be regarded as disproved. With this point settled, the old 

 acid theory glides easily into the new germ theory, and we 

 may recommence our studies from the new standpoint we 

 have gained, carrying with us all the facts that have been 

 developed to guide us on our way. 



In the study of this subject many new questions spring to 

 the front, and demand a hearing. Most of these have been 

 discussed in a former lecture ; but it now remains for us to 

 study their application to this particular subject. Before 

 doing this, however, it will be well for us to make a hasty 

 review of the discussions that have been had in comparatively 

 recent times on this point. 



THE GERM THEORY OF CARIES. 



Who may have first suggested that caries of the teeth is 

 caused by living germs, I have no definite knowledge. The 

 first work of importance upon this subject was by Lieber and 

 Rottenstein, in Germany, which appeared in 1868. These 

 gentlemen, in the prosecution of their studies of this question 

 came to the conclusion that caries must result from the 

 activity of micro-organisms through the production of acids. 



