INTIMATE NATURE OF MUSCULAR CONTRACTION 265 



condition of combination with the proteins of the sarcous element. 

 We have indeed certain micro-chemical evidence of the appearance 

 of potassium salts in the sarcous element during the state of activity 

 of the muscle. 



On the other hand, Bernstein ^has suggested that the changes 

 during muscular contraction are determined by alterations in surface 

 tension. If a little mercury be spilt on a plate the particles form 

 globules. They are kept from spreading themselves out in a thin 

 film under the influence of gravity in consequence of the surface 

 tension of the mercury. Any modification of the surface will alter the 

 tension, and therefore state of expansion, of the globule. Thus, if 

 the globule be in sulphuric acid it undergoes a certain amount of 

 polarisation, and becomes positively charged. By altering the charge 

 of such a globule we can change its shape, as is shown diagram- 

 matically in Fig. 92. If B represents the shape of the globule lying 



ABC 



FIG. 92. 



on the plate in some weak sulphuric acid, A will represent the shape 

 of the globule when it is connected with the negative pole of a battery, 

 while c will represent its shape when it is connected with the positive 

 pole of a battery, the other pole in each case being connected with 

 the acid. If we consider muscle as made up of a series of chains 

 of oval particles, a chemical change in the surface of these particles, 

 causing an increase of surface tension, will tend to make them 

 assume the globular shape, and will therefore cause a shortening 

 and thickening of the whole fibre. 



According to Schafer, contraction is associated with a flow of 

 the outer hyaline contents of the sarcous element into the tubular 

 structure forming the middle portion. Such a flow may be deter- 

 mined either by osmotic differences between the centre and periphery 

 of the sarcous element, or by a change in the surface tension obtaining 

 between the isotropic fluid at the ends and the anisotropic structures 

 in the centre of the muscle prism. 



It is impossible at present to decide between these different 

 theories. They have their use, however, in showing the possibility 

 of ' explaining ' a muscular contraction, i.e. of bringing it into a 

 series of phenomena the other members of which are already familiar 

 to us. They may therefore serve to point the direction which future 

 researches into the intimate nature of muscular contraction must take. 



