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/SCIENCE 



[N. S. Vol. XXXII. No. 824 



result of the formation of a septum in that 

 plane. In other words, the septum has first 

 to exist in order to allow the soaps and 

 lipoids to distribute themselves in a stream- 

 ing movement over its two faces. In 

 Brailsford Robertson's experiment this sep- 

 tum is provided in the thread. If, on the 

 other hand, surface tension is higher about 

 the nucleus in and immediately adjacent to 

 the future plane of division, then constric- 

 tion of the nucleus in that plane will take 

 place accompanied or preceded by an in- 

 ternal streaming movement in each half 

 towards its pole, and a consequent traction 

 effect on the chromosomes which are thus 

 removed from the equatorial plane. When 

 nuclear division is complete, then a higher 

 surface tension on the cell, itself limited to 

 the plane of division, would bring about 

 there a separation of the two halves, a eon- 

 sequent condensation on each side of that 

 plane of the substances producing the low 

 tension elsewhere, and thereby also the for- 

 mation of the two membranes in that plane. 

 In support of this explanation of the 

 action of surface tension as a factor in 

 division I have endeavored to ascertain if, 

 as a result of the Gibbs-Thomson principle, 

 there is a condensation of potassium salts 

 in the cytoplasm at the poles of a dividing 

 cell, that is, where surface tension, accord- 

 ing to my view, is low. The difficulty one 

 meets here is that, in the higher plant 

 forms, cells preparing to divide appear to 

 be much less rich in potassium than those 

 in the ' ' resting ' ' stage, and under this con- 

 dition it is not easy to get unambiguous 

 results, while in animal cells potassium may 

 even in the resting cell be very minute in 

 quantity, as, for example, in Vorticella, in 

 which, apart from the contractile stalk, it 

 is limited to one or two minute flecks in the 

 cytoplasm. Instances of potassium-hold- 

 ing cells undergoing division are, however, 

 found in the spermatogonia of higher ver- 



tebrates (rabbit, guinea-pig), and in these 

 the potassium is gathered in the form of 

 minute and thin caplike layers at each pole 

 of the dividing cell. 



This of itself would appear to show that 

 surface tension is less in the neighborhood 

 of the poles than at the equator of the 

 dividing cell, but I am not inclined to re- 

 gard the fact as conclusive, and a very 

 large number of observations to that end 

 must be made before certainty can be at- 

 tained. I am, nevertheless, convinced that 

 it is only in this way that we can finally 

 determine whether differences of surface 

 tension in dividing cells account, as I be- 

 lieve they do, for all the phenomena of cell 

 division. The difficulties to be encountered 

 in such an investigation are, as experience 

 has shown me, much greater than are to be 

 overcome in efforts to study surface tension 

 in cells under other conditions, but I am in 

 hopes that what I am now advancing will 

 influence a number of workers to take up 

 research in microchemistry along this line. 



I must now discuss surface tension in 

 nerve cells and nerve flbers. I have stated 

 earlier in this address that I hold that the 

 force concerned in the production of the 

 nerve impulse by the nerve cell is surface 

 tension. The very fact that in the repair 

 of a divided nerve fiber the renewal of the 

 peripheral portion of the axon occurs 

 through a movement — a flowing outward, as 

 it were — of the soft colloid material from 

 the central portion of the divided fiber, is, 

 in itself, a strong indication that surface 

 tension is low here and high on the cell 

 body itself. This fact does not stand alone. 

 I pointed out six years ago that potassium 

 salt is abundant along the course of the 

 axon and apparently on its exterior sur- 

 face, while it is present but in traces in the 

 nerve cell itself. In the latter chlorides 

 also are present only in traces, and there- 

 fore sodium, if present, is there in more 



