STUDY OF DISEASE 



activity. These operations depend in turn upon the activities 

 of remotely situated organs and tissues. Remote organs also 

 influence endocrinologically the function of liver in situ. In 

 addition, other influences, nervous, circulatory, and thermal, 

 remote in origin, may affect the functioning of the liver in its 

 normal habitat. 



Isolation and perfusion of this liver at once eliminates many 

 of these determinants of liver function. Humoral, including 

 hormonal, regulation is now determined by the experimenter, 

 not by the animal. Nervous regulation is usually lost. If the 

 liver is now sliced and shaken in a bath, further loss of organiza- 

 tion occurs. A fraction of the cells is necessarily incised, releas- 

 ing normally intracellular contents to the extracellular fluid. 

 The remaining cells are nourished in a rather haphazard fashion, 

 splashing about in a vessel instead of being supplied with a steady 

 flow of a regulated nutrient fluid pumped past each cell through a 

 system of venous sinuses. The process under study is confined 

 by the walls of the vessel, and unless special and elaborate condi- 

 tions are fulfilled, the concentration of substrate continuously 

 declines while that of product continuously rises. 



Homogenization of the tissue and disruption of the cellular 

 architecture is still a further insult. The microscopically visible 

 intracellular components, nucleus, mitochondria, nucleolus, 

 and microsomes, all bear, in the intact cell, geometrical relation- 

 ships to each other which are doubtless of functional significance 

 in the intact cell and which are destroyed in the process of homog- 

 enization. It may further be postulated that the submicro- 

 scopic particles, the molecules of the soluble enzymes, are likewise 

 in the intact cell not entirely free-swimming, but become so 

 when the cell is disrupted. It is possible that in the geographical 

 arrangement of enzymes within the cell resides the answer to 

 the typically polar or unidirectional character of epithelial 

 cells (14), and this is clearly lost in the process of homogenization. 

 Finally, the separation and purification of individual enzymes 

 from such a cell-free homogenate, though very rewarding, 

 inevitably divorces the enzyme from such inhibitory or excita- 



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