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The Vapour- Pressure Hypothesis of Contraction of Striated 



Muscle. 

 By H. E. Eoaf. 



(Communicated by Prof. C. S. Sherrington, F.R.S. Received April 16, — 

 Read June 18, 1914.) 



(From the Laboratory of Physiology, St. Mary's Hospital Medical School.) 



In 1854 Graham suggested that muscular contraction might be due to 

 ■osmotic influences (6). In 1878 FitzGerald suggested, on the other hand, that 

 muscular contraction might be due to changes in tension at the surface of the 

 fibrils of muscle (4). The application of these two hypotheses to the problem 

 of muscular contraction is still under investigation and discussion. 



Two principal objections have been raised to the osmotic explanation : — 

 (1) " Neither theoretically nor practically is it possible to construct a model 

 in the manner imagined by McDougall, which will, on being distended, 

 produce anything near the shortening which is observed in living muscle. 

 Living muscle may contract certainly to one-third of its length " (25). (2) ■' It 

 is impossible to conceive that water will flow into the sarcostyles from the 

 sarcoplasm, not in a third or a tenth of a second, only, but as in the case 

 of the wing muscles of insects, in less than one-two thousandth of a second" (10). 

 These two objections seem to be shared by Bernstein (2), Macallum (9), and 

 Sehafer (24). 



On the other hand, Macdonald (11), Macdougall (13), Pauli(15), and 

 Zuntz (27), support the hypothesis that muscular contraction is due to a rise 

 .of osmotic pressure. 



The structure of striated mammalian muscle is generally agreed to be a 

 ■series of fibrils suspended in sarcoplasm, the whole surrounded by the sarco- 

 lemma. The fibrils consist of alternating bands of anisotropous and isotropous 

 substance, the former corresponding to the portion of the fibril which is 

 contained in the dim band, the latter to the light band of the fibril (26). 

 Accepting this, the model that I wish to describe assumes that during 

 contraction lactic acid is formed, causing the portion of the fibril contained in 

 the dim band to swell and become spherical (see figure). Such a process is 

 exemplified by a parchment paper osmometer containing a protein solution. 

 If the osmometer is placed in a dilute solution of acid, the acid diffuses in and 

 -causes an increased absorption of water, with a rise of pressure. 



One explanation of this rise of pressure is that, as the acid diffuses into the 



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