THEORIES OF IMMUNITY. 



II. 



MetchnikofTs work is of the most remarkable 

 kind; painstaking and laborious to an extreme 

 degree, he has for more than twenty years put 

 forth a series of papers that are unsurpassed 

 for the closeness of reasoning and fertility of 

 device used to demonstrate his points. No ac- 

 count can be so satisfactory as his own, and the 

 present summary of his theory of the phagocytic 

 action of the tissue cells in securing immunity 

 is largely paraphrased from his own words. 

 (Metchnikoff. L'Immunite. Paris, 1901, pp. 

 541 et seq.) 



He began his studies on the germinative lay- 

 ers, and was able to explain satisfactorily to 

 himself the part played by the ectoderm and 

 the entoderm. While working in this direction 

 his attention was attracted to the intracellular 

 digestion occurring in many of the lower ani- 

 mals, and he was led to consider this property 

 as one common to the stock from which are 



derived all present known types of the animal 



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