MIRACLES OF SCIENCE 



spond to the best of their ability, producing a certain 

 amount of antitoxin and opsonin. Leucocytes gather 

 and prey on the invaders. But their best efforts 

 serve only to hold the parasites in check, not to over- 

 come them. 



But now comes the immunizator to the aid of the 

 local tissues. He makes a culture of bacteria of the 

 species in question; kills the bacteria by heating; and 

 injects a certain number into the tissue of the patient's 

 arm or leg. An intense reaction at once sets in at 

 the site of inoculation, and a relatively large quantity 

 of anti-bodies and opsonin is liberated into the blood 

 stream, and presently finds its way to the seat of 

 war, so to speak. These reinforcements may perhaps 

 turn the tide of what might otherwise have been a 

 hopeless battle. Cases of inflammation of the heart 

 have been cured in this way that until this new 

 method was introduced would have been beyond the 

 reach of medical skill. 



MIXED INFECTIONS' 



Of course the 'actual application of the new method 

 is not always so simple as this illustration may seem 

 to imply. For one thing, infections are very general- 

 ly "mixed," that is, due to several bacteria. Thus, 

 for example, the ulceration of the lungs that char- 

 acterizes tuberculosis, though primarily due to the 

 invasion of the tubercle bacillus, owes a large part of 

 its virulence to the coming of a quite different germ 

 called staphylococcus the germ that causes ordin- 

 ary abscesses and ulcerations is superficial tissues. 

 So it is often desirable in cases of tuberculosis to ap- 



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