44 JOURI^AL A^D PROCEEDINGS 



germs ma\' be prevented from spreading fnrther through the 

 lung ; " and so surrounding the field of battle, the connective 

 tissue cells of the organ are stimulated to proliferate and in so 

 doing build up an impenetrable wall around the diseased area. 



Or we have an inflammation of the appendix which threatens to 

 suppurate, rupture and infect the whole abdominal cavitj^ Then 

 the body throws out from the engorged blood vessels a serum con- 

 taining a tenacious substance called fibrin, which cements together 

 the tissues surrounding the trouble and thus prevents a more serious 

 infection of the general cavit}^ by locking up the dangerous area. 



But now suppose the body fluids do not contain a sufficient 

 amount of w^/wra;/ antitoxin or antibacterial substance and that con- 

 sequently a local inflammation is not capable of withstanding the 

 progress of the advancing enemy. The germs, or their to^^ins, or 

 both, get into the blood stream and are carried by it to all parts of 

 the system. How now? Surely the case is hopeless. The body 

 must at last give up the conflict. Not so. Again the vital con- 

 sciousness reasons : " This invasion is more serious than I at first 

 supposed. My ordinary defensive equipment is insufficient. I 

 must draw on the reserves." .^nd so the infection stimulates the 

 tissues to an increased production of policemen, a larger quantity 

 of antitoxin and a more abundant supply of antibacterial substance. 



What are these policemen that played such an important part 

 in immunity ? How and where are the antitoxin and the antibac- 

 terial substances produced and in what manner do they act ? And 

 here we must proceed carefully, for many are the theories ad- 

 vanced to explain the various phenomena of immunity. 



The policemen are the white blood corpuscles or leucocytes 

 and are of two kinds — those which have a single nucleus each or 

 lymphocytes, and the multinucleated forms. The lymphocytes are 

 found most active in chronic infections such as tuberculosis, while 

 in acute invasions, e.g , pneumonia, the multinucleated forms seem 

 to play the most important role. These cells have the power of 

 moving about in the body to places where they are most needed. 

 They act as the body scavengers, attacking, ingesting and destroy- 

 ing foreign elements — e.g., bacteria— that may invade the body. 



