THE RELATION OF BACTERIA TO DISEASE 51 



to the various cells around them, just as a tiny particle 

 of dust irritates the eye. All about the body cells are the 

 capillaries, flowing through which are the various blood- 

 cells suspended in a watery fluid called the blood-plasma. 

 The irritation produced by the staphylococci is at once 

 felt b}^ the blood-stream, and for a short time it flows 

 faster and the blood-vessels dilate, as though in this w-ay 

 to wash the irritant away. Undoubtedly there are many 

 times when this suffices, especially when the irritating 

 agent acts for only a short time and is very mild. If this 

 is not the case the blood-current slow^s, and now an inter- 

 esting process begins. The white blood-corpuscles (leuko- 

 cytes) make their way through the wall of the blood-vessel 

 and hunt out the offending bacteria. They act exactly 

 as though they were police officers going after a law 

 breaker. Accompanying the leukocytes is a ffow of serum 

 into the tissues, and this, as we shall see, contains sub- 

 stances which aid the leukocytes in their fight. If one 

 watches this process under a microscope one can see the 

 white blood-cells (leukocytes) actually engulf the invading 

 bacteria, sometimes taking up ten or a dozen bacteria.^ 

 But the fight is not yet over. It is all a question now 

 whether there are enough leukocytes to combat the bac- 

 teria, and whether the leukocytes can destroy the bac- 

 teria which they have engulfed. As a rule, some of 

 the leukocytes, instead of destroying the bacteria which 

 they have '^swallowed," are themselves destroyed by the 

 bacteria. 



Meantime, while some of the leukocytes are busy fighting 

 the bacteria, other cells are busy massing themselves 



^ In connection with this the student should study Fig. 37, which 

 shows a leukocvte filled with bacteria. 



