OCTOBBB 15, 1915] 



SCIENCE 



517 



of development of the contractile stress. 

 The degree of filling at the moment of con- 

 traction is thus the determining factor. 



That surface tension itself may be re- 

 sponsible for the energy given off in mus- 

 cular contraction was first suggested by 

 Fitzgerald in 1878, and it seems, from cal- 

 culations made, that changes at the contact 

 surface of the fibrillae with the sarcoplasm 

 may be capable of affording a sufficient 

 amount. The difficulties in deciding the 

 question are great, but, in addition to the 

 facts mentioned, there is other interesting 

 evidence at hand. It has been shown, by 

 Gad and Heymans, by Bernstein and others, 

 that the contractile stress produced by a 

 stimulus has a negative temperature coeffi- 

 cient. Within the limits of temperature 

 between which the muscle can be regarded 

 as normal, this stress is the greater the 

 lower the temperature. The same state- 

 ment was shown by Weizsacker (working 

 with A. V. Hill) to hold for the heat devel- 

 oped in the contractile stage. Now, of all 

 the forms of energy possibly concerned, 

 that associated with phase boundaries is 

 the only one with a negative temperature 

 coefficient. Another aspect of this relation 

 to temperature is the well-known increase 

 of the tonus of smooth muscle with fall in 

 temperature. 



It is tempting to bring into relation with 

 the change in surface tension the produc- 

 tion of lactic acid. In fact, this idea was 

 put into a definite statement by Haber and 

 Klemensievich in 1909 in a frequently 

 quoted paper on the forces present at phase 

 boundaries. The production of acid is 

 stated to alter the electrical forces at this 

 situation. This electrical charge involves 

 a change of surface tension, and it is this 

 change of surface tension which brings 

 about the mechanical deformation of the 

 muscle. Mines also has brought forward 

 good evidence that the production of lactic 



acid is responsible for the change of ten- 

 sion. As to how the lactic acid is set free, 

 and of what nature the system of high po- 

 tential present in muscle may be, we re- 

 quire much more information. The ab- 

 sence of evolution of carbon dioxide when 

 oxygen is not present shows that no oxida- 

 tion takes place in the development of 

 tension. There are other difficulties also in 

 supposing that this system present in rest- 

 ing muscle is of, a chemical nature. If the 

 energy afforded by the oxidation of carbo- 

 hydrate in the recovery stage is utilized for 

 the formation of another chemical system 

 with high energy content, the theory of 

 coupled reactions indicates that there must 

 be some component common to both systems. 

 It is difficult to see what component of the 

 muscle system could satisfy the conditions 

 required. On the whole, some kind of 

 system of a more physical nature seems the 

 most probable. If it be correct that the 

 oxidation of substances other than carbo- 

 hydrate, fat, for example, can afford the 

 chemical energy for muscular contraction, 

 as appears from the results of metabolism 

 experiments, a further difficulty arises in 

 respect to a coupled reaction. But the 

 question still awaits investigation. 



On the whole, I think that we may con- 

 clude that more study of the phenomena at 

 phase boundaries will throw light on many 

 problems still obscure. It would probably 

 not be going too far to say that the pecul- 

 iarities of the phenomena called "vital" 

 are due to the fact that they are manifesta- 

 tions of interchange of energy between the 

 phases of heterogeneous systems. It was 

 Clerk Maxwell who compared the transac- 

 tions of the material universe to mercantile 

 operations in which so much credit is trans- 

 ferred from one place to another, energy 

 being the representative of credit. There 

 are many indications that it is just in this 

 process of change of energy from one form 



