CORRELATION OF REFLEXES. 549 



COKKELATION OF REFLEXES AND THE PBINCIPLE OF 



THE COMMON PATH. 



By Professor C. S. SHERRINGTON, M.A., D.Sc, M.D., LL.D., F.R.S., 



PRESIDENT OF THE PHYSIOLOGICAL SECTION OF THE BRITISH ASSOCIATION. 



TDHYSIOLOGY studies the nervous system from three main points 

 -*- of view. One of these regards its processes of nutrition. Nerve- 

 cells, as all cells, lead individual lives, breathe, dispense their own 

 stores of energy, repair their own substantial waste, are, in short, liv- 

 ing units, each with a nutrition more or less centered in itself. The 

 problems of nutrition of the nerve-cell and of the nervous system, 

 though partly special to this specially differentiated form of cell life, 

 are, on the whole, accessible to the same methods as is nutrition in 

 other cells and in the body as a whole. 



But besides the essential functions common to all living cells, the 

 cells of the nervous system present certain which are specialized. 

 Among properties of living matter, one by its high development in the 

 nerve-cell may be said to characterize it. I mean the cell's transmis- 

 sion of excitement spatially along itself and thence to other cells. 

 This ' conductivity ' is the specific physiological property of nerve-cells 

 wherever they exist. Its intimate nature is, therefore, a problem co- 

 extensive with the existence of nerve-cells, and enters as a factor into 

 every question concerning the specific reactions of the nervous system. 



Thirdly, physiology seeks in the nervous system how by its ' con- 

 ductivity ' the separate units of an animal body are welded into a sin- 

 gle whole, and from a mere collection of organs there is constructed 

 an individual animal. 



This third line of inquiry, though greatly needing more data from 

 the second and the first, must in the meantime go forward of itself. It 

 is at present busied with many questions that seem special — hence its 

 work is generally catalogued as special physiology. But it includes 

 general problems. In the time before us I would venture to put before 

 you one of these. 



When we regard the nervous system as to this, which I would term 

 its integrative function, we can distinguish two main types of system 

 according to the mode of union of the conductors — (i.) the nerve-net 

 system, such as met in medusa and in the walls of viscera, and (ii.) 

 the synaptic system, such as the cerebro-spinal system of arthropods 

 and vertebrates. In the integrative function of the nervous system the 

 unit mechanism is the reflex. The chain of conduction in the reflex 



