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THE AMERICAN NATURALIST [Vol. LIV 



these more general tissue reactions, and thus they may 

 contribute to a physiology of tissues as contrasted with 

 the physiology of organs. Further experiments will 

 have to determine, how far the effect of the parenchyma 

 on the fibroblasts and blood vessels is a direct one and 

 how far secondary interactions between fibroblasts and 

 blood vessels enter into these reactions. 



These various substances (autosubstances, syngenesio-, 

 homoio- heterodifTerentials) have in addition to the func- 

 tions which concern the effect of cells upon each other 

 added functions of a specific nature. This is indicated by 

 the existence of specifically adapted substances like the 

 tissue coagulins which determine in a specifically adapted 

 manner the coagulation of the blood of various species. 4 



* Leo Loeb, Montreal Med. Journal, July, 1903; Firchow Archiv, 1904, 

 CLXXVI, 10; Biochem. Zcitschrift. 1010, XXVIII, 169. 



