CHAPTER X 

 MICKOBES— INFECTION— IMMUNITY * 



It would be beyond the scope of this work, and trenching 

 on the field of pure pathology, to give even a summary of 

 what is known regarding micro-organisms and the part 

 they play in disease processes. All that is here attempted, 

 is to place before the practical hygienist a brief account of 

 a question which directly bears upon some of the most 

 important problems with which he has to deal. 



In his search for the causes producing disease, and his 

 endeavours to combat these in the light of such exact 

 knowledge as we possess, the question of bacteria, infection, 

 and immunity, must ever be before him. He cannot move 

 without encountering them, nor can he succeed in stamping 

 out epizootic diseases without some knowledge of the life 

 history of bacteria and how their products may be turned 

 to useful advantage. 



The principle adopted in this chapter is to give a 

 grouping of bacteria, mentioning those responsible for 

 disease, and discussing how they obtain entrance to the 

 body where this is known ; also the conditions favourable 

 for their growth, how they succeed in infecting the animal, 

 and finally giving an outline of what is known as im- 

 munity, and how it is probably produced. 



* This chapter is from the pen of Dr. Theiler, Veterinary Bacte- 

 riologist to the Government of the Transvaal, to whom I am greatly 

 indebted. Dr. Theiler's researches in the field of pathology and his 

 intimate acquaintance with the veterinary aspect of these questions 

 are of especial value, and add an authority and interest to this chapter 

 which only a veterinary specialist can command. 



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