VACCINATION 147 



is rubbed some of the virus secured from previous 

 cases. After a few days this surface furnishes a yel- 

 lowish, watery material which contains the protective 

 stuff. This is gathered and mixed with glycerine, and, 

 after careful tests of its purity, is distributed to physi- 

 cians in small sealed glass tubes. This virus rubbed 

 on to a scratched surface of the human skin induces 

 a slight sore, sometimes accompanied by a little ma^ 

 laise, and then heals. 



By this process the liability to smallpox is very 

 greatly diminished, but the protection is reduced as 

 time passes, so that revaccination is necessary if the 

 fullest protection is to be secured. 



It is certain that smallpox is an infectious disease 

 induced by some form of micro-organism. But the 

 exact character of this is still unknown. Attempts to 

 cultivate it have thus far failed. It appears that the 

 unknown organism suffers diminution in virulence by 

 passing through the body of the relatively insuscepti- 

 ble calf, and in this condition, while incapable of in- 

 citing smallpox in man, is still potent to establish 

 immunity. 



A good deal of opposition has developed here and 

 there to vaccination even in recent times. This has 

 been based partly upon the fear lest foreign and 

 noxious material should be introduced into the body 

 along with the virus. But if it be carefully prepared, 

 this fear is groundless. While accidents are not im- 

 possible, the ill effects which now and then appear are 



