OCTOBEB 14, 1910] 



SCIENCE 



501 



minute quantities, while haloid chlorine is 

 abundant in the axon. Maedonald has also 

 made observations as to the occurrence of 

 potassium along the course of the axon, and 

 has in the main confirmed mine. We differ 

 only as to mode of the distribution of the 

 element in the axon, and the manner in 

 which it is held in the substance of the 

 latter ; but, whichever of the two views may 

 be correct, it does not affect what I am now 

 advancing. Extensive condensation or ad- 

 sorption of potassium salts in or along the 

 course of the axon, while the nerve cell 

 itself is very largely free from them, can 

 have but one explanation on the basis of 

 the Gibbs-Thomson principle, and that ex- 

 planation is that surface tension on the 

 nerve cell itself must be high while it is 

 low on or in its axon. 



The conclusions that follow from this are 

 not far to seek. We know that an electrical 

 displacement or disturbance of ever so 

 slight a character occurring at a point on 

 the surface of a drop lowers correspond- 

 ingly the surface tension at that point. 

 What a nerve impulse fundamentally in- 

 volves we are not certain, but we do know 

 that it is always accompanied by, if not 

 constituted of, a change of electrical poten- 

 tial, which is as rapidly transmitted as is 

 the impulse. When this change of poten- 

 tial is transmitted along an axon through 

 its syuaptic terminals to another nerve cell, 

 the surface tension of the latter must be 

 lowered to a degree corresponding to the 

 magnitude of the electrical disturbance 

 produced, and, in consequence, a slight dis- 

 placement of the potassium ions would 

 occur at each point in succession along the 

 course of its axon. This displacement of 

 the ions as it proceeded would produce a 

 change of electrical potential, and thus ac- 

 count for the current of action. The dis- 

 placement of the ions in the axon would 

 last as long as the alteration of surface 



tension which gave rise to it, and this would 

 comprehend not more than a very minute 

 fraction of a second. Consequently, many 

 such variations in the surface tension of 

 the body of the nerve cell would occur in a 

 second ; and, as the physical change con- 

 cerned would involve only the very surface 

 layer of the cell, a minimum of fatigue 

 would result in the cell, while little or none 

 would develop in the axon. 



It may be pointed out that in medullated 

 nerve fibers the lipoid-holding sheath, in 

 close contact as it is with the axon, must of 

 necessity maintain on the course of the lat- , 

 ter a surface tension low as compared with 

 that on the nerve cell itself, which, as the 

 synaptic relations of other nerve cells with 

 it postulate, is not closely invested with an 

 enveloping membrane. In non-medullated 

 nerve fibers the simple enveloping sheath 

 may function in the same manner, and 

 probably, if it is not rich in lipoid material, 

 in a less marked degree. 



What further is involved in all this, what 

 other conclusions follow from these obser- 

 vations, I must leave unexplained. It suf- 

 fices that I have indicated the main points 

 of the subject, the philosophical significance 

 of which will appear to those who will pur- 

 sue it beyond the point where I leave it. 



In bringing this address to a close I am 

 well aware of the fact that my treatment 

 of the subjects discussed has not been as 

 adequate as their character would warrant. 

 The position which I occupy imposes limits, 

 and there enters also the personal factor 

 to account in part for the failure to achieve 

 the result at which I aimed. But there is, 

 besides, the idea that in applying the laws 

 of surface tension in the explanation of 

 vital phenomena I am proceeding along a 

 path into the unknown which has been as 

 yet only in a most general way marked out 

 by pioneer investigators, and in conse- 

 quence, to avoid mistakes, I have been eon- 



