THE GERM THEORY OF CARIES. 109 



A question of great interest here, and the findings of Dr. 

 Miller make it doubly so, is the composition of the fluid that 

 is instrumental in the absorption of bone. I believe that I 

 have already referred to the opinion of Krause, and others 

 who regard it as containing lactic acid as its active principle. 

 Krause bases this opinion on the behavior of the tissue form- 

 ing this substance toward staining agents. From his experi- 

 ments, it seems quite certain that the substance has an acid 

 reaction, but the particular acid seems to me to be undeter- 

 mined. The action that we see in the absorption of the roots 

 of the teeth is not the action of lactic acid alone. This acid 

 dissolves the lime salts only, leaving the tissues of the tooth 

 behind in the normal form, as has been well shown by Magitot 

 and many other capable experimenters. 



This, of course, excludes the lactic acid as the exclusive 

 agent in the work. Nevertheless, the secretion may contain 

 this acid in combination with some other active principle. 



