lO MANUAL 03? BACTERIOLOGY. 



Even before this time men had sought to explain the phenom- 

 ena of infectious diseases by supposing the body to have been 

 penetrated by minute parasites, — for example, worms. The 

 spread of such diseases through a community from a single 

 center could readily be accounted for by the multipUcation of 

 a contagious element, itself alive {contagium vivum). With 

 increasing knowledge of the abundance of microscopic Kfe these 

 speculations took firmer hold. But long before their truth was 

 finally demonstrated great advances were made in the preven- 

 tion of infectious diseases. Much honor is due the clinicians, 

 whose accurate observations and foresight accomplished im- 

 portant results at an early day, working with what now seems a 

 very meagre knowledge of the facts. 



The production of immunity from small-pox by inoculation 

 was first practiced in oriental countries. The method had long 

 been in use in the East, when in 171 8 it was brought to the 

 notice of Europeans by Lady Montagu, wife of the EngHsh 

 ambassador at Constantinople. The procedure consisted 

 simply of the introduction of the virus of small-pox by 

 puncture of the skin. An attack of small-pox resulted, 

 which was usually much milder and far less dangerous than the 

 natural disease. 



Lady Montagu stated in a letter: "Every year thousands 

 undergo the operation ; and the French ambassador says pleas- 

 antly that they take the small-pox here by way of diversion, as 

 they take the waters in other countries." The mild attacks 

 that followed inoculation were, however, just as contagious to 

 other persons as the natural disease, so that the dangers of this 

 practice to the community were very great. 



A much better method was found in vaccination. At this 

 time a behef was current among fanners that a mild form of 

 disease, called cow-pox, acquired by milkers, furnished pro- 

 tection against small-pox. This belief was investigated and 

 introduced to the world by Edward Jenner. In 1796 he inocu- 



