' 



PRESIDENTIAL ADDRESS. 747 



To present an ample defence of all the parts of the thesis just advanced is 

 more than I propose to do in this address. That would take more time than is 

 customarily allowed on such an occasion, and I have, in consequence, decided 

 to confine my observations to outlines of the points as specified. 



It is not a new view that surface tension is the source of the muscular con- 

 traction. As already stated, the first to apply the explanation of this force as a 

 lactor in cellular movement was Engelmann in 1869, who advanced the view that 

 those changes in shape of cells which are classed as contractile are all due to 

 that force which is concerned in the rounding of a drop of fluid. The same view 

 was expressed by Rindfleisch in 1880, and by Berthold 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 Amoebce and Plasmodia 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 

 spreading protoplasm, which contains oils and soaps, over surfaces 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 protoplasm 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 produces a corresponding movement in the 

 drop at its periphery 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 Amoebce are brought about. In theee the 

 chylema or fluid of the foam-like structure in the protoplasm is alkaline, it con- 

 tiins 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 1S97, 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 whose wall 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 con- 

 traction. 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 longitu- 

 dinal 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 in the muscle fibre at rest the surface 

 must exceed somewhat 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 would not explain the large force generated in contraction, for the energy 

 liberated would be the product of the surface tension and the amount representing 



