In glycerine-extracted muscle fibers of the ABRM the tension remnant, peak tension and ATPase activity increase with the log of activation period. Moreover, the rate of tension rise after quick release of 0,08 L 0 appears to decrease with time elapsing between the beginning of activation and of release. Also in muscle this rate decreased more rapidly with time during administration of direct-than of rectangular current (r.a.e.) which the latter failing to result in catch.
The rate of tension rise following quick release (15 sec after commencement of stimulation) was the same for aeetylcholine (ACh) contracture and for r.a.e, contraction. However, the same two kinds--ACh and r.a.c.--give different peak tension prior to release (here referred to a difference in active-state). For active-states in which peak tension = 100%, the rates of tension rise observed in ACh contracture appear to decrease. 5-HT elevates peak tension in the 200 msec twitch to a maximum occurring at 10 -~ g/ml. Concentrations of 5-HT higher than 10 -7 g/ml again bring about a decrease in peak tension via a sharp fall in catch. On the basis of these experiments it may be inferred that the catch develops simultaneously with contraction.