Hypothesis of Contraction of Striated Muscle. 149 



the amount contained in the isotropous substance and concentrating the 

 remainder in the anisotropous substance. That is 



[0-025-0-01 (100-X)/100] . 100/X, 

 where X is the percentage of the whole muscle formed by the anisotropic 

 substance as calculated above. 



If we subtract the amount of uncombined lactic acid (0 - 01 normal) from 

 the above we have left - 06 normal and - 03 normal respectively, as the 

 amount of lactic acid as ionising salt in the anisotropic substance. These 

 would give osmotic pressures of 1018 mm. and 509 mm., both of which 

 exceed the 445 mm. which Bernstein states is the maximum required (2). 



By the formation of a lactic-acid salt of protein a negative potential would 

 be produced. This is apparently the explanation of the negative potential 

 produced when a muscle contracts (1, 3, 16, 19). The time relations of acid 

 production are such that the acid can be considered as the cause of contrac- 

 tion (23). 



There is one further point. It is claimed that if the contraction of 

 muscle is due to changes in surface tension one explanation suffices for 

 it and for amoeboid movement. Granting that amoeboid movement is due 

 to changes in surface tension, may it not be that the changes in surface 

 tension are due to electrical charges, the result of acid production ? Thus 

 amoeboid movement and muscular contraction may be related, but in a 

 different way from that advocated by those who claim that muscular con- 

 traction is due to changes in tension at surfaces of separation. We do not 

 yet know enough about unstriped muscle to suggest how its contraction is 

 brought about. 



The above outline gives a definite conception of muscular contraction 

 which accounts for all the known facts. If an equally tangible explanation 

 could be furnished based on surface-tension changes, the two hypotheses 

 might be compared one with another, and the two together might lead to 

 a conception closer to the truth than can be arrived at from either hypothesis 

 taken by itself. 



Summary of Conclusions. 



1. The contraction of striated muscle can be explained on the hypothesis 

 that lactic acid is set free, and that this combines with protein to form a salt, 

 with a consequent rise of osmotic pressure. 



2. Muscle can shorten by osmotic processes until its length is somewhere 

 between 37 and 3 per cent, of its original length (Table, columns 10 and 12). 



3. The osmotic process can occur in frog's sartorius in less than - 04 of a 

 second (Table, column 18). 



