1895.] On the Nature of Muscular Contraction. 417 



harmless. The muscle will no more be destroyed by stimulation 

 than a steamship will be destroyed by heating the furnaces. The 

 material of combustion only will be destroyed ; the vessel as a whole 

 remains unharmed. 



However likely it may thus seem that nature should avail herself 

 of these favourable terms on which mechanical work may result from 

 muscular heat, we have had up to the present time no direct proof that 

 this is actually the case, nor do we know in what way it takes place, 

 if in any. But I venture to think that the proof can now be given, 

 inasmuch as it is possible to demonstrate how, through the medium 

 of peculiar arrangements of the material of the muscle, a transforma- 

 tion of chemical energy into mechanical work by means of heat not 

 only can, but actually must, be brought about.* 



Muscular Structure in relation to Contractility. 



The Fibrils are the Seat of the Shortening Power. For this we need 

 firstly to pay attention to the peculiarities of the microscopical 

 structure of muscle. All muscular fibres of all animals are composed 

 chiefly of two parts : extremely thin, long, albuminous fibrils, and an 

 interfibrillar plasmatic substance, the so-called sarcoplasm. The 

 quantitative relations of both vary, but the fibrils always occur in 

 great number, forming very often the greatest part of the whole mass 

 of the muscle. They always run parallel to each other throughout 

 the length of the fibres. 



This fibrillar structure is also presented by all the other formed 

 contractile substances, such as the myonemata of Infusoria and of 

 other Protozoa, the cilia and vibrating membranes of cells, the tails 

 of spermatozoa, nay even, at least, when not in a state of contraction, 

 by the amoeboid protoplasm of Pelomyxa, Myxomycetes, and other 

 forms. 



Direct microscopical observation during life teaches us that the 

 fibrils, and not the sarcoplasm, are the seat of the shortening power. 

 The fibrils in a state of relaxation are long and thin, and often run 

 in winding curves, but grow short, thick, and straight, in conse- 

 quence of stimulation. The sarcoplasm passively follows their 

 movements. Moreover, completely isolated fibrils can shorten. 



The Fibrils are Contractile because they contain Doubly Refractive 

 Particles. Thus the question arises: can there be demonstrated in 

 the fibrils arrangements such that by means of them contractile force 

 may originate in a thermodynamic mode ? 



* The empirical foundations of the views developed in tins lecture will be found 

 in " Yersuche iiber Aenderungen der Form und der elastisclien Krafte doppel- 

 brechender G-ewebselemente unter chemischen und thermischen Einfliissen," in 

 the Appendix of my Memoir : ' TJeber den Ursprung der Muskelkraft ' (2te Auflage. 

 Leipzig. 1893. Pp. 5480), and in the literature cited in the same paper. 



VOL. LVII. 2 H 



