OCTOBEB 14, 1910] 



SCIENCE 



493 



surface tension between the surface of the 

 fiber and the surrounding fluid, and this of 

 itself has the effect of making the fiber 

 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 analogj^. In striated fiber, 

 on the other hand, the discs constituting 

 the light and dim bands have each a longi- 

 tudinal diameter which is an effect of its 

 surface tension, and this causes extension 

 of the fiber during rest. When a nerve 

 impulse reaches the fiber the surface ten- 

 sion of the discs is altered and there re- 

 sults a deformation of each involving a 

 shortening of its longitudinal axis and thus 

 a shortening of the whole fiber. 



According to Bernstein, in both smooth 

 and striated muscle fiber there is, in addi- 

 tion to surface tension, an elastic force re- 

 siding in the material composing the fiber 

 which, according to the conditions, some- 

 times opposes and sometimes assists the 

 surface tension. The result is that in the 

 muscle fiber at rest the surface must ex- 

 ceed somewhat that of the fiber in contrac- 

 tion. 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 ex- 

 plain the large force generated in contrac- 

 tion, for the energy liberated would be the 

 product of the surface tension and the 

 amount representing the diminution 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 actually manifested. To get 

 over this difficulty Bernstein postulates 

 that in muscle fibers, whether smooth or 



striated, there are fibrils surrounded by 

 sarcoplasma, and that each fibril is formed 

 of a number of cylinders or biaxial ellip- 

 soids singly disposed in the course of the 

 fibril, but separated from each other by 

 elastic material and surrounded by sarco- 

 plasma. Between the ellipsoids and the 

 sarcoplasma there is considerable surface 

 tension which prevents mixture of the sub- 

 stances constituting both. The excitation 

 through the nerve impulse causes an in- 

 crease of surface tension in these ellipsoids, 

 and they become more spherical. In conse- 

 quence the decrease in surface of all the 

 ellipsoids constituting 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 correspond- 

 ingly greater. The ellipsoids, Bernstein 

 explains, are not to be confused with the 

 discs, singly and doubly refractive in stri- 

 ated fiber ; for these, he holds, are not con- 

 cerned in the generation of the contraction, 

 but with the processes that make for rapid- 

 ity of contraction. The extension of a 

 muscle after contraction is due to the elas- 

 tic reaction of the substance between the 

 ellipsoids in the fibrils. Bernstein further 

 holds that fibrils of this character occur in 

 the protoplasm of AmcBboe, in the stalk of 

 Vorticella and in the ectoplasma of Sten- 

 tor, 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 fiber 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 pro- 



