DISEASE GERMS 9 



adjective to indicate that the particular micro-organism 

 under consideration is capable of producing disease, 

 for there are numerous micro-organisms which are en- 

 tirely harmless. The word pathogenic literally means 

 disease-producing ; a pathogenic micro-organism is 

 therefore a microscopic organism capable of produc- 

 ing disease. This sounds a little more scientific than 

 " disease germ," and it has seemed to me necessary to 

 spend a little time in explaining the meaning of the 

 term, as I may have occasion to use it from time to 

 time, although it is my intention to avoid the use of 

 technical terms as far as possible. 



When we say that a certain infectious disease is 

 due to a pathogenic micro-organism we have not 

 committed ourselves as to the characters of this dis- 

 ease germ. It may belong to the animal or the vege- 

 table kingdom ; it may be round or oval or spiral in 

 form ; it may be large or small, although microscopic. 

 But when I speak of the micrococcus of pneumonia 

 or the bacillus of typhoid fever, I am using terms 

 which convey much more definite information with 

 reference to the disease germs referred to, and before 

 proceeding any farther it will be desirable to make 

 the reader acquainted with the principal characters of 

 some of the best-known pathogenic micro-organisms. 

 Some of these belong to the animal and some to the 

 vegetable kingdom. Although so very minute and 



