150 THE STORY OF GERM LIFE. 



are killed at once, for these alexines act as anti- 

 septics, and common bacteria can no more grow 

 in the living body than they could in a solution 

 containing other poisons. Thus the body has a 

 perfect protection against the majority of bac- 

 teria. The great host of species which are found 

 in water, milk, air, in our mouths or clinging to 

 our skin, and which are almost omnipresent in 

 Nature, are capable of growing well enough in or- 

 dinary lifeless organic foods ; but just as soon as 

 they succeed in finding entrance into living human 

 tissue their growth is checked at once by these 

 antiseptic agents which are poured upon them. 

 Such bacteria are therefore not pathogenic germs, 

 and not sources of trouble to human health. 



There are, on the other hand, a few species of 

 bacteria which may be able to retain their lodg- 

 ment in the body in spite of this attempt of the 

 individual to get rid of them. These, of course, 

 constitute the pathogenic species, or so-called 

 "disease germs." Only such species as can over- 

 come this first resistance can be disease germs, 

 for they alone can retain their foothold in the 

 body. 



But how do these species overcome the poi- 

 sons which kill the other harmless bacteria ? 

 They, as well as the harmless forms, find these 

 alexines injurious to their growth, but in some 

 way they are able to counteract the poisons. In 

 this general discussion of poisons we are dealing 

 with a subject which is somewhat obscure, but 

 apparently the pathogenic bacteria are able to 

 overcome the alexines of the body by producing 

 in their turn certain other products which neu- 

 tralize the alexines, thus annulling their action. 

 These pathogenic bacteria, when they get into 



