108 THE MECHANISM OF LIFE 



therefore T 7f n = •»(), or T = 388-75° absolute, i.e. 115-75° C. 



Thus, in order to obtain an efficiency of 20 per cent, with 

 an ordinary thermic transformer, having a temperature of 38° 

 at the sink, we should need a temperature of over 115" C. 

 at the source. Such a temperature would be quite incompat- 

 ible with the integrity of living tissues, and we may therefore 

 conclude that the human organism is not a heat engine. 



We are indeed completely ignorant of the mode of trans- 

 formation of chemical into kinetic energy in the living 

 organism ; we know only that muscular contraction is accom- 

 panied by a change of form ; at the moment of transformation 

 the combustion of the muscle is increased, and during con- 

 traction the stretched muscular fibre tends to acquire a 

 spherical shape. It is this shortening of the muscular fibre 

 which produces the mechanical movement. The step which 

 we do not as yet fully understand is the physical phenomenon 

 which intervenes between the disengagement of chemical 

 energy and the occurrence of muscular contraction. Professor 

 d'Arsonval supposes that this missing step is a variation in 

 the surface tension of the liquid in the muscular fibre. The 

 surface tension of a liquid is due to the unbalanced forces of 

 cohesion acting on the surface layer of molecules. Under 

 the attraction of cohesion the molecules within the liquid are 

 in a state of equilibrium, being equally attracted in all direc- 

 tions, but those at the surface of the liquid are drawn towards 

 the centre. The resultant of these attractive forces is a 

 pressure normal to the surface, which is mechanically equiva- 

 lent to an elastic tension tending to diminish the surface. 

 In consequence of this surface tension the liquid has a tendency 

 to assume the form in which its surface area is a minimum, 

 ;'.<'. the spherical form. If such a sphere is stretched into a 

 cylinder or fibre by mechanical tension, it will shorten itself 

 when released ; and if by any means we increase the surface 

 tension of such a liquid fibre it will tend to assume a spherical 

 form and contract jus) as a muscular fibre does. The surface 

 tension of a liquid varies with its chemical composition; the 

 slightest chemical modification of a liquid alters the force of 



