66 THE STORY OF THE BACTERIA. 



they are thrown off in the form of a material 

 which we call pus. 



Now to come back to the bacteria which we 

 are studying. When these bacteria get into the 

 tissues, they may begin to grow, and as they 

 do so they produce a small amount of a poison 

 which we call a ptomaine, and this poison act- 

 ing injuriously on the tissues where it is 

 formed, the white blood-cells gather about it 

 just as they would about a wound. If the 

 bacteria continue to grow and multiply, the 

 white blood-cells may accumulate more and 

 more and die, the tissues may break down, 

 and so an abscess may be formed. Some- 

 times the germs get into the blood and are 

 carried to various parts of the body, and 

 wherever they lodge abscesses may be formed, 

 and this constitutes one of the most dreaded 

 forms of blood poisoning. 



Now what do the white blood-cells accom- 

 plish under these circumstances ? Many be- 

 lieve, although the matter has not been quite 

 settled yet, that when these bacteria get into 

 the tissues and begin to grow, the arrival of the 

 white blood-cells upon the scene signalizes the 



