130 THE STORY OF GERM LIFE. 



METHOD BY WHICH BACTERIA PRODUCE 

 DISEASE. 



Since it was first clearly recognised that cer- 

 tain species of bacteria have the power of pro- 

 ducing disease, the question as to how they do 

 so has ever been a prominent one. Even if they 

 do grow in the body, why should their presence 

 give rise to the symptoms characterizing dis- 

 ease ? Various answers to this question have 

 been given in the past. It has been suggested 

 that in their growth they consume the food of 

 the body and thus exhaust it ; that they produce 

 an oxidation of the body tissues, or that they 

 produce a reduction of these tissues, or that 

 they mechanically interfere with the circulation. 

 None of these suggestions have proved of much 

 value. Another view was early advanced, and has 

 stood the test of time. This claim is that the 

 bacteria while growing in the body produce poi- 

 sons, and these poisons then have a direct action 

 on the body. We have already noticed that bac- 

 teria during their growth in any medium produce 

 a large number of biproducts of decomposition. 

 We noticed also that among, these biproducts 

 there are some which have a poisonous nature ; 

 so poisonous are they that when inoculated into 

 the body of an animal they may -produce poison 

 ing and death. We have only to suppose that the 

 pathogenic bacteria, when growing as parasites in 

 man, produce such poisons, and we have at once 

 an explanation of the method by which they give 

 rise to disease. 



This explanation of germ disease is more than 

 simple theory. It has been in many cases clearly 

 demonstrated. It has been found that the bac- 



