August 23, 1912] 



SCIENCE 



253 



undergo a more or less evident coagulation. 

 The most striking instance known to me is that 

 of the swimming plates of ctenophores; these 

 structures, when immersed in pure isotonic 

 solutions of sodium salts, exhibit for a short 

 time an abnormally accelerated contractile 

 rhythm accompanied by a progressive coagu- 

 lation of the normally transparent contractile 

 substance; this coagulation is the more rapid 

 and complete the more energetic the con- 

 tractile movements. Piitter in his recently 

 published " Vergleichende Physiologie " cites 

 (p. 456) a number of instances where con- 

 traction of muscle is accompanied by a visible 

 coagulation of the muscle-substance. In 

 vertebrate muscle the coalescence of colloidal 

 particles — assuming it to take place — does not 

 normally lead to visible coagulation during 

 contraction. But it is characteristic of this 

 tissue that the contraction is instantly and 

 automatically reversed unless a rapid and 

 rhythmical process of stimulation is con- 

 tinued. This peculiarity, which is perhaps 

 the most remarkable property of this tissue, 

 is favorable to, or at least quite consistent 

 with, the view that a temporary coalescence of 

 the colloidal particles occurs at each stimula- 

 tion — due to a depolarization of the sur- 

 face of the particles, simultaneously with 

 a depolarization of the plasma-membrane 

 of the entire cell — ^and that this coal- 

 escence is instantly reversed by the automatic 

 return of the membrane to its normal polar- 

 ized condition. If, however, the plasma mem- 

 brane becomes permanently depolarized, as in 

 consequence of any marked and permanent 

 increase in ionic permeability (such as occurs 

 during cytolysis), the coalescence of colloidal 

 particles becomes permanent, and a visible 

 coagulation, typically accompaned by a 

 permanent shortening or " contracture," fol- 

 lows. Such an effect is produced if a frog's 

 muscle is immersed in physiological salt solu- 

 tion containing saponin or other cytolytic 

 substance. If the muscle is first sensitized by 

 esrposure for a few minutes to a pure isotonic 

 solution of a sodium salt, such as iodide, the 

 cytolytic action of the saponin is accelerated; 

 the contraction is thus rendered quicker and 



more energetic and the degree of coagulation 

 is greater; i. e., the energy of the contraction 

 shows a distinct parallelism with the energy 

 of the coagulative process in the muscle-sub- 

 stance. It might be maintained that the 

 coagulative change is merely a secondary con- 

 sequence of the cytolysis, and has no direct 

 connection with the contraction, but when these 

 facts are taken in conjunction with the others 

 cited in this paragraph the indications seem 

 strong that the ultimate process causing con- 

 traction is essentially the same as that which 

 — if carried far enough — Pleads to coagulation 

 of the colloids. As already pointed out, the 

 latter process is due to fusion of colloidal par- 

 ticles to form larger aggregates; what causes 

 the union appears to be heightened surface-ten- 

 sion resulting from diminished electrical 

 surface-polarization; the increased tension 

 then draws the particles together and thus 

 performs a certain mechanical work. Simi- 

 larly in the contractile tissue; within each 

 fibril the colloidal particles or submicrons — 

 which presumably are already in contact or 

 cohere since the whole fibril forms a solid gel- 

 like system — draw together more closely dur- 

 ing contraction in consequence of a sudden 

 increase in their surface-tension. This coales- 

 cence occurs only within each fibril, not be- 

 tween adjacent fibrils, hence the motion of 

 displacement of the particles is virtually lim- 

 ited to the direction of the long axis and in 

 consequence the whole fibril shortens. As the 

 coalescence of the particles proceeds the active 

 surface-area steadily decreases, and with it 

 the contractile force ; hence this force is great- 

 est at the beginning of contraction and di- 

 minishes as the muscle shortens. 



We assume therefore that in contraction the 

 colloidal particles, especially those of the 

 anisotropic segments, draw together or coal- 

 esce. There is, in other words, a clumping or 

 flocking of the particles, which is most rapid 

 and energetic in those regions where the par- 

 ticles are most numerous and closest together. 

 In so doing they displace the more fluid inter- 

 stitial substance. This incidental displace- 

 ment of fluid is as necessary an accompani- 

 ment of the act of contraction as the coales- 



