750 ' TRANSACTIONS OV SECTION I. 



time. In support of this explanation may be cited the fact that the current of 

 action in muscle precedes in time the contraction itself — that is, the electrical 

 response of the stimulus occurs in the latent period and immediately before the 

 contraction begins. 



It may, however, be postulated, on the other hand, that the chemical changes 

 occur in those parts of the dim band immediately adjacent to the light bands, 

 and as a result the tension of the terminal surfaces may be increased, this 

 resulting in the shortening of the longitudinal axis of the dim band and the 

 displacement laterally of the contents. This would imply that the energy of 

 muscle contraction comes primarily from that set free in the combustion process, 

 and not indirectly as involved in the former explanation. 



Whatever may be the cause of the alteration in surface tension, there would 

 seem to be no question of the latter. The very alteration in shape of the dim- 

 band in contraction makes it imperative to believe that surface tension is con- 

 cerned. The redistribution of the potassium which takes place as described in 

 the contracting fibrils of the wing muscles of the scavenger beetle can be 

 explained in no other way than through the alteration of surface tension. 



In the smooth muscle fibre potassium is also present and in close association 

 throughout with the membrane. When a fresh preparation of smooth muscle is 

 treated so as to demonstrate the presence of potassium, the latter is shown in 

 the form of a granular precipitate of hexanitrite of sodium, potassium, and 

 cobalt in the cement substance between the membranes of the fibres. In the 

 smooth muscle fibres in the walls of the arteries in the frog the precipitate 

 in the cement material is abundant, and its disposition suggests that it plays 

 some part in the role of contraction. Inside of the membrane potassium occurs, 

 but in very minute quantities, which, with the cobalt sulphide method, gives a 

 just perceptible dark shade to the cytoplasm as a whole. Microchemical tests 

 for the chlorides and phosphates indicate that the cytoplasm is almost wholly 

 free from them, and consequently there is very little inorganic material inside of 

 the fibre. Chlorides and phosphates, but more particularly the former, arc 

 abundant in the cement material, and their localisation here would seem to 

 indicate that the potassium of the same distribution is combined chiefly as 

 chloride. 



In smooth muscle fibre, then, the potassium is distributed very differently 

 from what it is in striated fibre, and on first thought it seemed difficult to postulate 

 that the contraction could be due to alterations of surface tension. This, how- 

 ever, would appear to be the most feasible explanation, for the potassium salts 

 in the cement substance might be supposed to shift their position under the 

 influence of electrical force so as to reach the interior of the membranes of the 

 fibres, in which case the surface tension of the latter would be immediately 

 increased and the fibre itself would in consequence at once begin to contract. 

 The slowness with which this shifting into, or absorption by, the membrane of 

 the potassium salts would take place would aleo account for the long latent period 

 of contraction in smooth muscle. 



It is of interest here to note that the potassium ions have the highest ionic 

 mobility (transport number) of all the elements of the kationic class, except 

 hydrogen, which are found to occur in connection with living matter. Its value 

 in this respect is half again as great as that of fodium, one-eighth greater than 

 that of calcium, and one-seventh greater than that of magnesium. This high 

 migration velocity of potassium ions would make the element of special service 

 in rapid changes of surface tension. 



Loew has pointed out that potassium in the condensation processes of 

 the synthesis of organic compounds has a catalytic value different from that of 

 sodium. For example, ethyl aldehyde is condensed with potassium salts to 

 aldol, with sodium salts to crotonic aldehyde (Kopf and Michael). Potassium 

 is, but sodium is not, effective in the condensation of carbon monoxide. When 

 phenol is fused with potassium salts condensation products like diphenol are 

 produced, but when sodium salts are used the products are dioxybenzol and 

 phloroglncin (Barth). It is, therefore, not improbable that potassium, along 

 with those properties which come from its ionic mobility, has a special value in 

 the metabolism of the dim bands of striated muscle fibre and in the condensa- 

 tion synthesis which characterise the chromatophors of Protophyta (Spirogyra, 



