THEORIES OF IMMUNITY. 



in the same blood after coagulation there would 

 appear marked bactericidal powers. 



If further experiments serve to support these, 

 and to show that under ordinary circumstances 

 there is no bactericidal property in the circu- 

 lating blood, it can easily be seen how impor- 

 tant this would be for Metchnikoff 's theory of 

 the formation of such a property in the cells as 

 the result of vital action. 



Metchnikoff goes on, in his summing up, to 

 say that; There is only one constant element in 

 immunity, — either natural or acquired, — and 

 that is the property of phagocytosis. The ex- 

 tent and importance of this factor cannot be 

 denied. It has been fully shown that the phago- 

 cytes are sensitive cells that react against mor- 

 bific agents whether they are organized or not. 

 These cells englobe the bacteria and absorb the 

 soluble substances. They seize upon bacteria 

 that are living and able to exercise their hurtful 

 properties, and subject them to the action of 

 their cellular contents which are able to kill and 

 digest the bacteria, or at least prevent their 



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