PARKE S LISTj ETC. 



which may be carried and communicated by 

 floating dust. 



II. — It is claimed that diseases placed in class 

 two may be carried and communicated by float- 

 ing dust or taken into the system in water. The 

 "air or water home" diseases, so-called. 



III. — *Inoculation as a rule, is the means of Inoculation. 

 communication of diseases mentioned in class 

 three. 



IV. — ^A surface lesion is said to be necessary Lesion. 

 for the communication of diseases in class four. 

 When this lesion is present the disease is com- 

 municable by direct inoculation or may be 

 transmitted through the air. (By "lesion" we 

 mean a wound, hurt, or other local alteration 

 of tissue from a higher to a lower condition.) 



V. — In class five a surface lesion is not neces- 

 sary and the disease is communicable either by 

 direct inoculation or through the air. 



It must be borne in mind, however, that Authorities 

 authorities differ as to the mode of entrance Differ, 

 of some of the bacteria and that theories change 

 as new light is thrown on the subject. The 

 science of bacteriology is still rapidly pro- 

 gressing. 



The alimentary canal, the respiratory tract, 

 the genital tract, the mucous membranes. 



* By inoculation we mean the introduction of a specific 

 virus into the system. 



49 



