338 



THE AMERICAN MONTHLY 



[N"ov 



of bacteria there is often no decay of sufBcient import- 

 ance to attract attention, unless the enamel or dentine be 

 examined by the aid of the microscope and differential 

 stains. Then the surface enamel and dentine will show 

 bacteria adhering, and even penetrating for a considera- 

 ble distance the structure of the tooth. 

 a- 



The above figure shows the penetration of nitrate of 

 silver into enamel partly decomposed by bacteria, a, Im- 

 mune layer of enamel deeply stained. Taken from a 

 young lady's mouth in which white decay was rapidly de- 

 stroying the teeth. This tooth was treated three years 

 ago to nitrate of silver without filling. Decay stopped in 

 all teeth thus treated. Tooth crowned. 



The extent of decomposition thus produced by bacteria 

 may be as I have stated only visible through the micro- 

 scope or differential staining. (See fig. 1, a : and fig, 2). 

 For example, when a tooth presenting the white chalky 



