CHAPTER II 



DISEASE GERMS 



TTAVING ascertained that infection results from 

 * * the introduction of living " disease germs " into 

 susceptible individuals, it will be well to give some 

 consideration to these agents of infection. The term 

 disease germ is a popular one and is used to desig- 

 nate any micro-organism capable of giving rise to an 

 infectious disease. The word micro-organism, which 

 I shall have frequent occasion to use, may require a 

 little explanation. By an organism we mean an or- 

 ganic structure which has been built up by vital pro- 

 cesses. It may be a plant or an animal, it may be 

 complex or simple, large or small, but it must, at one 

 time at least, have been endowed with life. A micro- 

 organism is simply a microscopic organism, and being 

 microscopic it is an organism of very simple structure, 

 usually consisting of a single cell (" unicellular micro- 

 organism "). When using the word micro-organism 

 with reference to a disease germ, we must use an 



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