CHAPTEE VI 



INFECTIOUS DISEASES AND MICROBES, ETC. 



'THE study of disease-gerrns by the new and 

 accurate methods of bacteriology has led to a 

 clearer and better understanding of the manner in 

 which, at any rate, some of the infectious diseases 

 spread. While it was understood previous to the 

 identification of their precise cause that some 

 spread directly from individual to individual (e.g. 

 small-pox, scarlet fever, diphtheria), others were 

 known to be capable of being conveyed from one 

 individual to another indirectly, i.e. through ad- 

 hering to dust, or being conveyed by water, milk, or 

 by food-stuffs (e.g. cholera, typhoid fever). But we 

 are now in a position to define and demonstrate 

 more accurately the mode in which infection can 

 and does take place in many of the infectious 

 diseases. By these means we have learned to 

 recognise that the popular distinction between 

 strictly contagious and strictly infectious diseases 

 the former comprising those diseases which spread, 

 as it were, only by contact with a diseased indi- 

 vidual, while in the latter diseases no direct contact 

 is required in order to produce infection, the disease 



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