ON SOME PHYSICAL MANIFESTATIONS OF LIFE 55 



from objections such as we have mentioned ; namely, by assuming 

 that chemical, not thermal conditions determine the absorbtion of fluid 

 by the anisotropic substance. The action of the nerve upon the muscle 

 might consist in facilitating a chemical change which increases the 

 absorption of water by the anisotropic substance of the muscle. 



2. QUINCKE'S THEORY OF PROTOPLASMIC MOTION 



The thermodynamic conception of muscular contraction has been 

 abandoned by many authors, and the surface energy has been con- 

 sidered in its stead as the cause of muscular contraction and work. 

 D'Arsonval, Imbert, and more recently Bernstein, have tried to offer a 

 hypothesis of this kind. We shall understand these hypotheses better 

 if we first consider Quincke's theory of protoplasmic motion.* 



When a drop of oil is put on the surface of water which is in contact 

 with air, the oil spreads in an extremely thin layer at the limit between 

 water and air. This process continues until a film of oil exists between 

 water and air. The conditions for the spreading of the oil on the sur- 

 face of the water are as follows: 

 the particle of oil O at the left end 

 of the oil drop (Fig. 7) is under the 

 influence of three surface tensions 



which pull at it in three different - v _~^rr^ _~ WAITER 



directions, OA, OB, and OC, and 

 with different force. One is the 



surface tension between air and water, which tends to pull the 

 particle from O in the direction OA. The second is the surface 

 tension OB at the limit of oil and air, which tends to pull the 

 particle O in the direction of the tangent OB from O. The third 

 force is the surface tension at the limit of oil and water, which tends 

 to pull the particle in the direction of the tangent OC from O. The 

 surface tension at the limit of water and air is greater than the sum of 

 the surface tensions at the limit between oil and air, and oil and water. 

 The surface tension between air and water is 8.25 mg., between oil and 

 air 3.76 mg., and between oil and water 2.73 mg. The particle O will 

 therefore be pulled toward the left ; and the same will happen with the 

 next particle of oil, until the surface water air is substituted by the 

 surface oil air. 



These phenomena of spreading are accompanied by motions in the 

 neighboring particles of liquid. If oil spreads at the surface of water, 



* Quincke, Sitzungsbtrichtc der Berliner Akadtmic der Wissensch., p. 791, 1888. 



