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. In a 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 

 involved 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- 



