1895.] On the Nature of Muscular Contraction. 423 



muscular force can give a sufficient explanation of this fact. On the 

 basis of our theory, on the contrary, it can "be predicted, because 

 every influence which augments the doubly-refractive power must 

 raise the power of contraction. 



Now, von Ebner has proved experimentally that the doubly refrac- 

 tive power of tendons and also, between certain limits, of muscles, 

 increases with the load. The same is the case with fibres of elastic 

 tissue and with caoutchouc, and here also the contractile power 

 increases with the load. 



The differences of force which depend on the load are by no means 

 insignificant. According to Fick the lifting heights for 5, 8, and 

 10 gr. were, with a muscle of Anodonta, related to each other as 

 "8*3 : 10 : 16*3. With E strings, swollen in hot water, I obtained, 

 when heating them from 20 to 80 C., at an initial load of 5 gr., a 

 contractile power of but 55 gr. ; at a load of 50 gr. one of 80 gr. ; 

 and at a load of 90 gr. one of about 120 gr. 



For E strings swollen in lactic acid of 0'25 per cent, the rates of 

 power, corresponding with the initial tensions of 5, 90, and 125 gr., 

 amounted to about 100, 125, and 154 gr. A strip of elastic tissue, 

 2 mm. thick, heated at 80 C., gave for an initial tension of 10 gr., at 

 which the double refraction of fibres is just beginning to be per- 

 ceptible, a power of but 61 gr., for 100 gr. one of 162 gr., for 

 185 gr. of initial tension, at which double refraction is very strong, 

 one of 238 gr. A strip of vulcanised caoutchouc, 2 mm. thick, 

 which, unloaded and hence singly refractive, did not, even when 

 heated to 100 C., tend at all to become shorter, developed with an 

 initial load of 90 gr., put on at 20 C., a contractile power of 110 gr. 

 at a temperature of 80 C., while at the same time a strong power of 

 double refraction had been acquired by it. 



Now, it is true, that Heidenhain has found that at least in the 

 stimulated striated muscles not only mechanical energy but also 

 the development of heat and the formation of lactic acid increase 

 together with initial tension. But, according to his experiments, 

 mechanical energy increases much more rapidly than does the pro- 

 duction of heat. This difference at least might be explained by the 

 influence of extension on the doubly-refractive power. An influence 

 of extension on chemical action may very well be associated with the 

 influence on double refraction, as a consequence of the changes in the 

 local arrangement of the thermogenic particles which are produced 

 by the extension. Such changes must be effected to a considerable 

 degree, even when the shortening of the muscle is prevented by 

 resistance (isometric contraction of Fick), and especially in the case 

 of striated muscles, to which Heidenhain's statements refer. For 

 not only fibrils, interfibrillar substance, and sarcolemma, but also the 

 singly and the doubly-refractive portions of the fibrils differ much 



