CHAPTER IV. 
THE RELATION OF BACTERIA TO DISEASE. 
In the preceding chapter our consideration has been 
given largely to the chemical effects of bacteria on dead 
organic substances. Here we have to consider the 
growth of bacteria in living bodies and the results of © 
such development. While it is true that there is a 
great difference between living and dead matter, and 
that, therefore, the living animal cannot be considered 
as merely a quantity of organic and inorganic material, 
to be used for food for bacterial growth, still the fact 
that bacteria do increase in the living body shows 
that its tissues are under certain conditions a suitable 
nutrient soil for their growth. Ina sense, therefore, 
we are warranted to consider the living body as we do 
any other medium for bacterial growth, remembering, 
however, that beside the chemical nature, temperature, 
etc., of its tissues, micro-organisms have also to reckon 
with the mysterious influence of life with which all 
parts of the body are endowed. In the production of © 
disease by micro-organisms there are two main factors 
involyed—viz., the power to elaborate poison and the 
ability to multiply. No known variety of bacterial cell 
has as a single organism the ability to produce enough 
poison to do appreciable injury in the body, nor is there 
any variety which if it multiplied in the body to the 
full extent to which it is capable under favorable con- 
