NOTES B^OR BEGINNERS IN MICROSCOPY. 14-7 



duced on ihe body at large, Pain does not require peripheral 

 terminal cells, like the special senses; for if you knock the skin off 

 your knuckles, the spot will be painful when touched, at the same 

 time as it will have lost the delicate sense of touch. Moreover, 

 painful impressions may arise in the deeply-seated organs of the 

 body. What is the good of pain ? It warns the Central Nervous 

 System of something locally wrong and ensures rest for the painful 

 part, thus giving the first and best chance for repair to take place. 

 When our first ancestor first injured himself, we can picture his 

 astonishment at feeling this new sensation, his quickly discovering 

 that movement increased his pain, and his consequent resting of 

 the wounded part till it healed. Pain, then, has some value in 

 this colony we call man ; it is the message from some outlying 

 units that they are out of working order and must be given rest, 

 whatever their rest may mean. 



1Rote6 for BcQinnerB in flDicroscop^. 



By R. N. Reynolds, M.D. 



Micro-Organisms of the Teeth. 



THOUSANDS, if not tens of thousands, of bacteria of various 

 kinds and motions may be plainly seen swimming about in 

 each field of the microscope by employing the following 

 method : — 



Place on any good microscope a Wenham paraboloid and a 

 good half-inch objective. 



The specimen may then be taken from the natural teeth of 

 any human mouth by placing the points of curved forceps or 

 other instrument near the gum between two of the lower back 

 teeth, then giving one scrape upward. A pin-head size of tartar 

 will be found on the forceps, and should be broken up in a drop 

 of water on a glass slip. On this lay a cover-glass and place on 

 the stage of the microscope. When fully illuminated by the 

 paraboloid, the pieces of tartar will appear as white as snow, but 

 we shall see no bacteria ; next turn the mirror until the light is 

 beginning to lessen, and we shall soon reach a point at which we 



