SURFACE TENSION 



137 



to 18 C. the maximal tension was found to be 205 g. Surface 

 energy is the only possible form of energy that could be associated 

 with muscular contraction which has a negative temperature 

 coefficient. 



In dealing with surface tension (Chap VI.) it was pointed out 

 that most physical and chemical actions are accelerated by increase 

 of temperature, while surface energy is diminished as tempera- 

 ture rises. 



A glance at Fig. 24 may make it clear how surface energy may 

 be made to do work. 



A wire frame is made, to one side of which is attached a silk 

 thread. Over the whole area is a film of soap. The thread M 



A B 



FIG. 24. Frame of wire enclosing a Soap Film. 

 In A there is a loop of fine silk floating in the film. 

 In B, the film enclosed by the loop has been broken. (After Van der Mensbrugghe.) 



takes up an indifferent position as shown in (A) as the surface 

 tension at the interface between F and S is exactly balanced by 

 the internal energy of F ^internal energy of S. If now the film 

 is broken inside F, say by pricking with a needle, M tends to 

 become a circle. That is, the internal energy of S is increased 

 relatively to that of F. However it is brought about, the result 

 is an increase in the surface tension at the interface F S, i.e. the 

 thread. It is of value to note that it is not necessary for the film 

 to be broken. Theoretically, all that is necessary is a difference 

 in internal energies on the two effective sides of the thread, the 

 lower internal energy being inside the loop. Further, no matter 

 how slight the difference on the two sides of the thread the movement 

 would be maximal. 



Muscle consists of a number of long fibrillae immersed in 

 sarcoplasm. The membranes of the fibrillae may be represented 

 by the thread mentioned above, the protoplasm of fibril and 

 sarcoplasm as the soap film. Anything which causes a difference 



