138 THE STORY OF GERM LIFE. 



cilli everywhere. Some of the obscure diseases 

 known as blood poisoning appear to be of the same 



general nature, 

 these diseases re- 

 sulting from a very 

 general invasion of 

 the whole body by 

 certain pathogenic 

 bacteria. 



In general, then, 

 we see that the so- 

 called germ diseas- 

 es result from the 



FIG. ^.-Anthrax bacillus (splenic <* Ct j n r U P n . the 



fever). body of poisons 



produced by bac- 

 terial growth. Differences in the nature of these 

 poisons produce differences in the character of 

 the disease, and differences in the parasitic pow- 

 ers of the different species of bacteria produce 

 wide differences in the course of the diseases and 

 their relation to external phenomena. 



WHAT DISEASES ARE DUE TO BACTERIA? 



It is, of course, an extremely important matter 

 to determine to what extent human diseases are 

 caused by bacteria. It is not easy, nor indeed 

 possible, to do this to-day with accuracy. It is 

 no easy matter to prove that any particular dis- 

 ease is caused by bacteria. To do this it is neces- 

 sary to find some particular bacterium present in 

 all cases of the disease ; to find some method of 

 getting it to grow outside the body in culture 

 media; to demonstrate its absence in healthy ani- 

 mals, or healthy human individuals if it be a hu- 



