THEORIES OF IMMUNITY. 



Metchnikoff (I. c.) summarizes the present 

 status of affairs in substance, as follows: The 

 theory of Ehrlich is not in opposition to the 

 theory of phagocytosis. Ehrlich considers that 

 the bacteriolytic ferments as well as the cyto- 

 toxic-alexines or complements (called cytases by 

 Metchnikoff) exist in a soluble condition in the 

 circulating blood plasma, whilst Metchnikoff 

 believes that they are normally present in the 

 interior of the phagocytes. This has nothing 

 to do with the Ehrlich theory in regard to the 

 receptors or lateral chains, which considers the 

 antitoxines and certain other anti-bodies (inter- 

 mediary substances) as products detached from 

 the cells and having an affinity for the toxines 

 and bacterial products. 



The theory of phagocytosis seeks to establish 

 the part played by the cells in the destruction 

 of the bacteria. It premises that the vital phe- 

 nomena of the phagocytes, such as motility, 

 sensitiveness (chemiotaxis), and voracity are 

 essential conditions for relieving the tissues from 

 the bacteria, for the true bacterial ferment is 

 contained within the phagocytes except when 

 phagolysis has occurred. The destruction of 



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