160 THE GERM THEORY OF DISEASE. 



Microscopic examination showed that these cultures con- 

 tained an organism similar to those found in the deeper layers 

 of carious dentine, and which remained constant in their char- 

 acters. Chemical examination, which seems to have been 

 very carefully conducted, showed the acid produced to be 

 lactic acid. This acid has been shown to be capable of de- 

 composing the teeth by M. Magitot and many others. Yet 

 Dr. Miller goes still further, and by placing sections of 

 dentine in his culture fluids that he has infected, finds that 

 they are decomposed by the acid formed ; while such sections 

 placed in such fluids not infected are not changed. Thus he 

 not only proves that an acid is formed, but that the acid is 

 formed in sufficient amount to destroy the dentine. 



This, when compared with the best experimentation previ- 

 ously had, marks a great advance. One point seems to have 

 been gained. One organism has been traced thus far, and 

 may now be said to have been proven to be able to produce 

 certain of the phenomena of decay. But this is not all. 

 There is much yet to be done. True, one other point is 

 spoken of by Dr. Miller. All who have made a careful 

 study of caries know that there is a peculiar enlargement of 

 the tubules, which is not seen in dentine softened by acids 

 alone. Dr. Miller has been looking for this also, and not 

 without success; for in some sections of dentine exposed to 

 the action of the cultures, he found the organisms crowding 

 into the tubules, and tells us that he also found them en- 

 larged, as in natural caries of the teeth in the mouth ; indeed, 

 that he had before him veritable caries, artificially produced. 



This delineation of results of experimentation must have 

 great weight in the settling of the problems at issue ; especi- 

 ally if they are confirmed by other competent observers. 

 There is nothing in these experiments that is not in harmony 

 with known facts, unless it be the widening of the tubules by 



