116 IRRITABILITY 



unintelligible. But how are we to interpret these secondary 

 results from a physical standpoint ? First of all, it must be stated 

 that we do not know of such hypertrophy following activity in 

 unicellular organisms, but only in the tissues and organs of multi- 

 cellular forms, in muscles, nerve cells, glands, etc. In the cell 

 community of the vertebrates, however, the studies on the rela- 

 tions between activity and the blood supply of the particular 

 tissue or organ furnish a physical interpretation for the exist- 

 ence of the functional hypertrophy. The active portions show 

 a dilation of the blood vessels, therefore an increased supply of 

 blood and consequently an increase in the circulation of lymph. 

 In other words: the supply of nourishment to the individual cell 

 and the removal of the metabolic products in a unit of time is 

 increased. The preceding discussion of the dependence of the 

 conditions of equilibrium upon the quantitative relations of the 

 reacting substances makes it clear that under these conditions a 

 metabolic equilibrium on a higher quantitative level must occur; 

 that is, the living substance must increase in amount just as in 

 the inanimate example the absolute amount of the sethylacetat 

 increases if more alcohol and acetic acid are introduced to an 

 equal degree. Some time ago^ I expressed the opinion that the 

 increase of the blood supply in a functionally active organ must 

 be based on a physical self-regulation, which takes place as a 

 result of the fact that metabolic products of the tissue cells 

 influence the cells of the vessel walls in that part, so that the 

 vessels dilate and more lymph is formed. In the meantime this 

 has been proved to be indeed the case. Schwarz und Lemberger' 

 and Ishikawa^ have shown that especially the weak acids, which 

 are produced in larger amount as a result of strong activity of the 

 cells, bring about vessels' dilation. By the demonstration of this 

 highly important process of self-regulation the last link has been 

 added for the physical understanding of the hypertrophy of 

 activity of the tissue cells by continued functional excitation. 



1 Max Verworn: "Die cellularphysiologische Grundlage des Gedachtnisses." Zeitschr. 

 f. allgem. Physiol. Bd. VI, 1907. 



2 Schwarz und Lemherger : "t^ber die Wirkung Kleinster Sauremengen auf die 

 Blutgefasse." Pfliigers Arch. Bd. 141, 1911. 



3 These investigations have not yet been published. 



