INFECTION IN DISEASE. 743 



2.— INFECTION IN DISEASE. 



By C. E. BARNARD, M.D. ' 



It is my intention in this short paper to give a hare outline 

 of some of the more recent advances that have been made in 

 the direction of the causes of infection. 



Generally speaking, the word " infection " means the trans- 

 mission of a disease from one individual to another, either )jy 

 direct or indirect contact. The word " contagion " is some- 

 times used in a similar sense, but originally it meant the 

 conveying of disease by contact only. 



Formerly, before the present more exact methods of 

 research were invented, little or nothing was known of the 

 medium by Avhich infection was supposed to be carried. The 

 poisonous matter or contagium was, however, regarded as 

 being endowed with vital energy, as it was known to bs 

 capable, when once introduced, of developing in the system, 

 and of causing considerable constitutional disturbance. 



The idea has long ])een prevalent that infectious diseases 

 owed their existence and progress to the j^resence of some 

 ferment setting up a process of fermentation in the system, 

 and hence they have l)een grouped together under the term 

 "zymotic diseases." The morbific material setting up the 

 disease was supposed to act similarly to a ferment in the 

 process of fermentation, and to be derived from an infected 

 person . 



When fermentation was found to be due to the action of 

 microscopic cells which multiplied rapidly during the jn-oeess, 

 and likewise that microscopic organisms were found to be 

 always more or less intimately associated with the zymotic 

 diseases, the analogy was regarded as complete. Thorough 

 search was then made for micro-organisms in the blood and 

 tissues of persons suffering from infectious diseases, and, as 

 only particular forms were found in each disease, the specific 

 micro-organisms were looked upon as the ultimate cause of 

 infection. 



It was not until the year 1876, when Koch discovered the 

 means of isolating and cultivating in nutrient media outside 

 the body a bacillus, the B. anthracis, that the life history and 

 morphology of other bacilli could be ])roperly studied. This 

 discovery laid the foundation of the modern science of 

 Bacteriology. 



The micro-organisms are the smallest living beings with 

 which we are acquahited, and are composed of a living 



