THE OPSONIC THEORY. 



more how prophetic were the words of Pasteur the 

 Pasteur. Step, by step biologists, bacteriolo- Prophet. 

 gists, pathologists and therapeutists have been 

 drawing nearer the goal, each investigator 

 profiting by the errors of his predecessors — 

 each coming a step nearer the truth. 



Years ago Metchnikoff promulgated his 

 theory of Phagocytosis. Since his time it has 

 been known that when bacteria enter the 

 tissues of the body the system at once en- 

 deavors to combat their invasion by sending 

 vast numbers of white blood cells to meet the 

 enemy. To that mysterious power of attrac- 

 tion which exists between the invading bac- 

 teria and the leucocytes, or phagocytes, we 

 have applied the term chemiotaxis. The pha- 

 gocytes have the power under certain circum- Chemiotaxis. 

 stances of picking up the microbes, ingesting 

 them and killing them. Metchnikofif, believ- 

 ing that the leucocytes were the only active 

 elements in the process of phagbcytosis, held 

 that the fluid portion of the blood was merely 

 an indifferent medium. Others taking up the 

 work found that the serum is far from being 

 inactive or indifferent. They found that the 

 invading bacteria are in many cases victorious 

 and overcome the defensive leucocytes. And 

 this led to the question why either the bacteria 

 on the one hand or the white blood corpuscles 

 on the other hand are not always victorious, 



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