1895.] On the Nature of Muscular Contraction. 429 



fifths of the initial length. At 15 C. they exert, in the first case, 

 forces of about 80 gr., in the second of about 110 gr. With initial 

 tensions of 105, 335, and 450 gr., forces of 226, 365, and 496 gr. respec- 

 tively were produced by swelling in distilled water at 15 C. ; and by 

 imbibing a 0'25 per cent, solution of lactic acid at initial tensions 

 of 5, 215, and 425 gr. forces were exerted of 115, 350, and 490 gr. 

 respectively, i.e., forces very much higher than a muscle of the same 

 thickness can produce during tetanus. Even in a watery solution of 

 only O'l per cent, of lactic acid, the strings contract to about 70 per 

 cent., as also in highly-diluted acetic and hydrochloric acid or in 

 potash. 



Upon neutralisation or dilution the old length and volume return. 

 The doubly-refractive fibrils, or the sarcous elements of muscles, 

 contract considerably, also under the same conditions, swelling at the 

 same time ; this is the case even with muscles which have been killed 

 in alcohol. In such instances I measured in the striated fibres of 

 insects, distinguished by especially long sarcous elements, shortenings 

 to 50 per cent, and more. 



Since, according to many inquirers, lactic acid is formed during 

 the rigor of striated muscles, and at all events the reaction of the 

 muscular plasma grows acid, the doubly-refractive elements must 

 necessarily swell more and tend to shorten, and this contraction will 

 remain until the acid has been neutralised or removed by diffusion. 



Similar results will be obtained in other cases of rigor characterised 

 by shortening and by the production of much acid, such as the ordinary 

 rigor mortis, the rigor produced by distilled water, the rigor which is 

 caused by excessive stimulation, &c. Nay, in a bloodless muscle 

 even a physiological stimulation, when sufficiently strong and long, 

 may be expected to produce a lasting shortening, on account of the 

 'gradually increasing acidity. Indeed, the well-known incomplete 

 relaxation of such muscles seems to me to be a symptom of this 

 chemical contraction, as it may be called, in contrast with the thermal. 



In a muscle in which the blood stream is maintained this will not 

 so easily take place, not even under a strong and prolonged stimula- 

 tion, because the acid is immediately neutralised or removed through 

 diffusion. Even in the isolated, bloodless muscle the acid, which is 

 produced by stimulation, may, in the beginning at least, be rendered 

 harmless through the very large quantity of non-acid fluid imbibed 

 by the muscle. Consequently we must expect in these cases an 

 immediate and complete relaxation after contraction. The facts agree 

 absolutely with these suppositions. 



It is, perhaps, not unnecessary to remark that all these observa- 

 tions would also hold good if the material affecting the turgescence 

 were not lactic acid, but another substance arising during the chemical 

 action in the muscle, e.g., water. 



