THEORIES OF IMMUNITY. 



and that in all its aspects it resembled very 

 closely the phenomena of intracellular digestion 

 going on in the epithelial cells lining the digest- 

 ive tract of very many of the inferior animals. 

 At Messina, in 1882-1883, he set himself to 

 secure definite evidence of this fact, and did so 

 by proving that these cells (of the mesoderm) 

 seize upon foreign bodies of very varying nature 

 by their living prolongations, and that some of 

 these foreign substances undergo a true diges- 

 tion in the interior of these ameboid cells. 



Then the idea suggested itself to him that this 

 digestive function, evidently fixed in the meso- 

 dermic cells, might also play a part in many of 

 the vital processes of the animal. Working 

 from this point of view, he was able to demon- 

 strate that during the complicated metamorpho- 

 sis of echinoderms, such as the synaptera, the 

 mesodermic ameboid cells played a part in the 

 atrophy of many embryonic organs. 



He had never studied medicine, but he was 

 struck at one time by an exposition by Cohnheim 

 of the facts of the latter's theory of inflammation. 

 The facts as presented impressed him strongly, 



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