PROPAGATION OF PHYSIOLOGICAL CHANGE 489 



by other factors also. Bethe has shown that prolonged 

 stimulation is followed by an alteration in staining capacity 

 with certain basic dyes, a circumstance which may have no 

 more meaning than an alteration in physical state. It is true 

 that this absence of chemical evidence may be ascribed to the 

 minute quantity of change involved, and to the swift flight of 

 the nervous impulse. 



It is no doubt true that the maintenance of life in the nerve- 

 fibre is dependent upon chemical factors. As is the case with 

 all intracellular material, the continuance of its function is 

 ultimately dependent upon a complex of chemical and physical 

 states to which the cell-nucleus, nutriment, oxygen, and the 

 removal of waste products such as carbonic acid are essential. 

 Doubtless, too, this complex is affected by narcotics in some 

 cases, in a manner to be assigned to the inhibition of certain 

 essential chemical processes. No doubt also drastic interference 

 with this complex may produce an abnormal physico-chemical 

 state in which symptoms of fatigue become obvious, as in the 

 instance of the effects of aconitine observed by Waller, chloro- 

 form by Garten, lack of oxygen by Frohlich. But here we 

 have our fingers upon the very acme of lability. This is the 

 tissue from which many of the conceptions of lability of living 

 matter are derived. It is significant that here of all places we 

 should have to hunt so desperately for instances of chemical 

 change. There is, then, excellent reason why, on a basis of 

 experimental fact, nerve should not be used in illustration of 

 the value of any purely chemical concept of function. 



Thus that rapid propagation of physiological change from 

 point to point which is the leading function of nerve, but is 

 by no means confined to nerve, is doubtless always due to the 

 conveyance of a physical change. The train of gunpowder is 

 apparently a simile to the contrary, but I believe I am right 

 in insisting that in this case the explosion of each segment in 

 turn is due to a rise in temperature. That physical factors are 

 alone responsible for the similar excitation of each successive 

 piece of nerve has been laboriously proved by a study of the 

 action of every admissible form of stimulus. Efficient physical 

 forms of stimulation are, the incidence of light, a rise of 

 temperature, a slight mechanical shock, pressure, a sudden fall 

 of electrical potential, sometimes a fall of temperature, some- 

 times a rise of electrical potential, sometimes the removal of 



