148 THE STORY OF GERM LIFE. 



be entirely sufficient to seize such a foothold, and 

 then these by multiplying may soon become in- 

 definitely numerous. To protect itself, therefore, 

 the human body must destroy every individual 

 bacterium, or at least render them all incapa- 

 ble of growth. Their marvellous reproductive 

 powers give the bacteria an advantage in the bat- 

 tle. On the other hand, it takes time even for 

 these rapidly multiplying beings to become suf- 

 ficiently numerous to do injury. There is thus an 

 interval after their penetration into the body 

 when these invaders are weak in numbers. Dur- 

 ing this interval the period of incubation the 

 body may organize a resistance sufficient to ex- 

 pel them. 



We do not as yet thoroughly understand the 

 forces which the human organism is able to array 

 against these invading foes. Some of its meth- 

 ods of defence are, however, already intelligible 

 to us, and we know enough, at all events, to give 

 us an idea of the intensity of the conflict that is 

 going on, and of the vigorous and powerful forces 

 which the human organism is able to bring against 

 its invading enemies. 



In the first place, we notice that a majority of 

 bacteria are utterly unable to grow in the human 

 body even if they do find entrance. There are 

 known to bacteriologists to-day many hundreds, 

 even thousands of species, but the vast majority 

 of these find in .the human tissues conditions so 

 hostile to their life that they are utterly unable to 

 grow therein. Human flesh or human blood will 

 furnish excellent food for them if the individual 

 be dead, but living human flesh and blood in some 

 way exerts a repressing influence upon them which 

 is fatal to the growth of a vast majority of spe- 



