SURFACE TENSION 167 



determined its absolute force, embedded it in celloidin, and found 

 the average radius of each fibril to be 9.994 X 10~^ cm. From 

 this he calculated that in a square centimeter there would be 

 31,460,000 fibrils, which, on the basis of data for elasticity and 

 absolute force, gives 0.022 gram as the value of the surface tension 

 of the fibril at its fibril-sarcoplasm interface — a value near that 

 of oil at an oil-water interface. Such hypotheses are tested out 

 by experimentally measuring the force generated by muscle 

 contraction. This should equal the energy liberated as a result 

 of change in surface tension. The energy is the product of the 

 surface tension and the diminution of the surface due to con- 

 traction. If the surface energy liberated is found to be too small, 

 a more complex structure of the muscle fiber is postulated in 

 order to get more surface. Such an assumption is justified, but 

 there is no conclusive evidence to support the theory as a whole. 

 Other postulates are just as convincing. Electrocapillary forces 

 are at play. Differences in electrical potential cause deformation 

 {e.g., as in the case of a mercury drop) and, by thus altering form, 

 produce shortening, or contraction. Osmotic pressure {i.e., 

 turgor) and imbibition pressure are forces available to actuate 

 muscles. Plant "muscles" (motor cells) are "pumped up" 

 with water, establishing turgor pressure, which is later relieved 

 when the "muscle" collapses (and the plant wilts). Animal 

 muscle may have the structure of a sponge or jelly, a porous 

 meshwork, into and out of which fluid passes. While the various 

 theories on the part that surface tension plays in muscular con- 

 traction are largely speculative, it is possible that surface tension 

 is yet a factor in muscle action. 



Macallum, in an exposition on surface tension and vital 

 phenomena, closes with a speculation on the physical nature of 

 psychic functions. He says that sensation, that is to say, the 

 nerve impulse, is fundamentally and primarily a result of altera- 

 tion in the surface tension of nerve cells and their processes. 

 He believes that he can thus explain anesthesia and narcotism. 

 Chloroform, ether, and alcohol lower the surface tension of cells, 

 especially nerve cells, and so make them incapable of receiving 

 or transmitting a nerve impulse. Memory itself, Macallum 

 concludes, may arise from the adjustment of the surface tension 

 of the cells in centers of the cerebral cortex. (Actually, we know 

 nothing about the mechanism of memory.) 



