THE MICROSCOPE. 165 
interesting to know how he succeeds in observing these specimens 
alive, and in distinguishing a growing extremity from the extremity 
that does not grow. Transmitted light is necessary, even to see 
them at all, and the difficulty would be greater in case of such sec- 
tions as these, for the earthy matter has not been dissolved out; 
therefore the preparations would not be as transparent as in the case 
of microtome sections. Besides, this fungi must certainly be a uni- 
cellular plant. In such a case it would grow in all parts alike, and 
not having organs of special function, one part would look like 
another. Nor is there a chance to divide an object so small into 
extremeties. It would be interesting to know in what respect it dif- 
fered, one extremity from another. This is certainly a new specie, 
and Dr. Miller should have given us an accurate description of all 
its parts. 
Another difficulty is the acid that is given off at the growing 
extremity. How could he determine it to be an acid, or see a flow of 
liquid from an object so small? He must have a good microscope. 
I have examined a great many sections of teeth, from perfectly 
sound teeth to all stages of decay, but have never seen anything like 
microfungi in any part except the structureless material taken from 
the cavities of carous teeth. Of course this is only negative evidence, 
but there is a quantity of it. 
A hard section of a tooth was placed in a bottle containing some 
distilled water and infected with decomposing organic matter. An 
examination was made from time to time. Bacteria at certain stages 
was found in abundance, but the tooth section remained unaffected; 
no micro-organisms were to be found within its tissue and the surface 
retained its polish. Even the small amount of organic matter it 
contained was no temptation to these desperadoes. 
It is well known that after death decomposition soon sets in, in 
the soft parts, but the last to succumb to the action of the elements 
is the teeth. Then it is in the mouth only that the conditions exist 
favorable to decay. If bacteria or other organisms have anything to 
do with the process, why not do the work out of the mouth, especially 
when the conditions most favorable for their existence are arranged? 
My conclusion is that caries of the teeth is entirely a chemical 
process. 
The predisposing causes of caries are (1) inherited defects in 
the structure; such as flaws and extreme thinness in the enamel, 
especially on approximal surfaces and in the crevices of molars and 
bicuspids, where fluids are held by capillary attraction. (2) One 
other matter to be taken into consideration is the influence of impact 
