THE GERM THEORY OP CARIES. 161 



the crowding in of the organisms. It is known, by previous 

 experiment, that this widening is not caused by the lactic acid 

 as it exists dissolved in the surrounding medium. And I think 

 very few will be willing to concede that the organisms can 

 accomplish this by physical force. This point requires further 

 investigation, and its study will doubtless lead to further dis- 

 coveries. However, we think it may be explained in advance; 

 at least, the effort may serve to direct experimentation. 



In a previous lecture we have dwelt at some length upon 

 the digestive fluids of living organisms. Unexpectedly we 

 find use for these ideas now, for they were written before we 

 saw Dr. Miller's last article. I have explained how it is that 

 dead bone, roots of the temporary teeth, ivory driven into 

 the flesh, catgut ligatures, sponge, etc., are dissolved and 

 removed by a soluble ferment. I have also shown that the 

 soluble ferment of the yeast plant has been found and proven : 

 also that of ammoniacal fermentation; and how plants* take 

 up otherwise insoluble substances. Now this widening of the 

 tubules is a conceded fact. It is also shown that it is not 

 done by the lactic acid in case of other experiments ; nor can 

 it be done by the physical force of the organisms; but it can, 

 in all probability, be done by the digestive fluid of the organ- 

 ism. The conditions for this work of the digestive fluid is 

 the same as that of the granulations in widening the meshes 

 of the sponge and finally removing the last of it. As yet 

 no such soluble ferment has been demonstrated in connection 

 with this organism; but theoretically it must exist, and if 

 Dr. Miller should undertake to search for it, he will be able 

 to demonstrate it speedily, and determine its co-operation in 

 producing some of the phenomena of decay. At least, de- 

 termine its capabilities.* This organism cannot be said to 



* Since the above was written Dr. Miller has also reported the finding 

 of another micro-organism that he thinks capable of producing caries. 



