448 



NATURE 



[October 6, 1910 



in 1886, who explained the protoplasmic streaming in 

 cells as arising in local changes of surface tension between 

 the fluid plasma and the cell sap, but he held that the 

 movement and streaming of Amoebae and PlasmoditE are 

 not to be referred to the same causes as operate in the 

 protoplasmic streaming in plant cells. Quincke in 1888 

 applied the principle of surface tension in explaining all 

 protoplasmic movement. In his view the force operates, 

 as in the distribution of a drop of oil on water, in spread- 

 ing protoplasm, which contains oils and soaps, over sur- 

 faces in which the tension is greater, and as soap is 

 constantly being formed, the layer containing it, having 

 a low tension on the surface in contact with water, will 

 as constantly keep moving, and as a result pull the proto- 

 plasm with it. The movement of the latter thus generated 

 will be continuous, and constitute protoplasmic streaming. 

 In a similar way Biitschli explains the movement of a 

 drop of soap emulsion, the layer of soap at a point on 

 the surface of the spherule dissolving in the water and 

 causing there a low tension and a streaming of the water 

 from that point over the surface of the drop. This pro- 

 duces a corresponding movement in the drop at its peri- 

 phery and a return central or axial stream directed to 

 the point on the surface where the solution of the soap 

 occurred and where now a protrusion of the mass takes 

 place resembling a pseudopodium. In this manner, 

 Biitschli holds, the contractile movements of AmoebjE are 

 brought about. In these the chylema or fluid of the 

 foam-like structure in the protoplasm is alkaline, it con- 

 tains fatty acids, and, in consequence, soaps are present 

 which, through rupture of the superficial vesicles of the 

 foam-like structure at a point, are discharged on the free 

 surface and produce there the diminution of surface tension 

 that calls forth currents, internal and external, like those 

 which occur in the case of the drop of oil emulsion. 



The first to suggest that surface tension is a factor in 

 muscular contraction was D'Arsonval, but it was Imbert 

 who, in iSq7, directly applied the principle in explanation 

 of the contractility of smooth and striated muscle fibre. 

 In his view the primary conditions are different in the 

 former from what obtain in the latter. In smooth muscle 

 fibre the extension is determined, not by any force inside 

 it, but by external force such as may distend the organ 

 (intestine, bladder, and arteries) in the wall of which it 

 is found. The " stimulus " which causes the contraction 

 increases the surface tension between the surface of the 

 fibre and the surrounding fluid, and this of itself has the 

 effect of making the fibre tend to become more spherical 

 or shorter and thicker, which change in shape does occur 

 during contraction. He did not, however, explain how 

 the excitation altered the surface tension, except to say 

 that its effect on surface tension is like that of electricity, 

 with which the nerve impulse presents some analogy. In 

 striated fibre, on the other hand, the discs constituting the 

 light and dim bands have each a longitudinal diameter 

 which is an effect of its surface tension, and this causes 

 extension of the fibre during rest. When a nerve impulse 

 reaches the fibre the surface tension of the discs is altered, 

 and there results a deformation of each involving a 

 shortening of its longitudinal axis, and thus a shortening 

 of the whole fibre. 



According to Bernstein, in both smooth and striated 

 muscle fibre there is, in addition to surface tension, an 

 elastic force residing in the material composing the fibre 

 which, according to the conditions, sometimes opposes and 

 sometimes assists the surface tension. The result is that 

 m the muscle fibre at rest the surface must exceed .some- 

 what that of the fibre in contraction. In both conditions 

 the sum of the two forces, surface tension and elasticity, 

 must be zero. In contraction the surface tension increases, 

 and with it the elasticity also. Taken as a whole, this 

 %yould not explain the large force generated in contrac- 

 tion, for the energy liberated would be the product of the 

 surface tension and the amount representing the diminu- 

 tion of the surface due to the contraction. As the latter 

 IS very small the product is much below the amount of 

 energy in the form of work done actuallv manifested. 

 To get over this difiicultv, Bernstein postulates that in 

 muscle fibres, whether smooth or striated, there are fibrils 

 surrounded by sarcoolasma, and that each fibril is formed 

 of a number of cylinders or biaxial ellipsoids singlv dis- 



posed in the course of the fibril, but separated from each 

 other by elastic material and surrounded by sarcoplasma. 

 Between the ellipsoids and the sarcoplasma there is con- 

 siderable surface tension which prevents mixture of the 

 substances constituting both. The excitation through the 

 nerve impulse causes an increase of surface tension in 

 these ellipsoids, and they becoine more spherical. In con- 

 sequence, the decrease in surface of all the ellipsoids con- 

 stituting a fibril is much greater than if the fibril were to 

 be affected as an individual unit only by an increase of 

 surface tension, and thus the surface energy developed 

 would be correspondingly greater. The ellipsoids, Bern- 

 stein explains, are not to be confused with the discs, singly 

 and doubly refractive in striated fibre ; for these, he holds, 

 are not concerned in the generation of the contraction, but 

 with the processes that make for rapidity of contraction. 

 The extension of a muscle after contraction is due to the 

 elastic reaction of the .substance between the ellipsoids in 

 the fibrils. Bernstein further holds that fibrils of this 

 character occur in the protoplasm of Amoebae, in the stalk 

 of Vorticella, and in the ectoplasma of Stentor, and this 

 explains their contractility. 



It may be said in criticism of Bernstein's view that 

 his ellipsoids are from their very nature non-demonstrable 

 structures, and, therefore, must always remain as postu- 

 lated elements only. Further, it may be pointed out that 

 he attributes too small a part to surface tension in the 

 lengthening of the fibre after contraction, and that the 

 elasticity which muscle appears to possess is, in the last 

 analysis, but a result of its surface tension. 



As regards Quincke's explanation of protoplasmic move- 

 ment and streaming, as well as of muscular contraction, 

 Biitschli has shown that it is based on a mistaken view 

 of the structure of the cell in Chara and other plant 

 forms in which protoplasmic streaming occurs. Biitschli 's 

 own hypothesis, however, is defective in that it postulates 

 a current in the fluid medium just outside the ."Amoeba 

 and backward over its surface, the existence of which 

 Berthold denies, and Biitschli himself has been unable to 

 demonstrate, even with the aid of fine carmine powder 

 in the fluid. He did, indeed, observe a streaming in the 

 water about a creeping Pelomyxa, but the current was in 

 the opposite direction to that demanded by his hypothesis. 

 Further, his failure to demonstrate the occurrence of the 

 postulated backflow in the water about the contracting 

 or moving mass of an Amoeba or a Pelomyxa makes it 

 difficult to accept the hypothesis he advanced to explain 

 that backflow, namely, that rupture of peripheral vesicles 

 (Wabcn) of the protoplasm occurs with a consequent dis- 

 charge of their contents (proteins, oils, and soaps) into 

 the surrounding fluid. Surface tension, further, on this 

 hypothesis, would be an uncertain and wasteful factor in 

 the life of the cell. On a priori grounds, also, it would 

 seem improbable that this force should be generated out- 

 side instead of inside the cell. 



One common defect of all these views is that they made 

 only a limited application of the principle of surface 

 tension. This w'as because some of its phenomena were 

 unknown, and especially those illustrating the Gibbs- 

 Thomson principle. With its aid and with the knowledge 

 of the distribution of inorganic constituents in animal and 

 vegetable cells that microchemistry gives us we can make 

 a more extended application of surface tension as a 

 factor in cellular life than was possible ten years ago. 



In regard to muscle fibre this is particularly true, and 

 microchemistry has been of considerable service here. 

 From the analyses of the inorganic constituents of striated 

 muscle in vertebrates made by J. Katz and others we 

 know that potassium is extraordinarily abundant therein, 

 ranging from three and a half in the dog to more than 

 fourteen times in the pike the amount of sodium present. 

 How the potassium salt is distributed in the fibre was 

 unknown before 1004, in which year, by the use of a 

 method, which I had discovered, of demonstrating the 

 potassium microchemicallv, the element was found 

 localised in the dim bands. Later and more extended 

 observations suggested that in the dim band itself, when 

 the muscle fibre is at rest, the potassium is not uniformly 

 distributed, and it was found to be the case in the wing 

 muscles of certain of the Insecta — as, for example, the 

 scavenger beetles — in which the bands are broad and con- 



NO. 2136, VOL. 84] 



