Interdigitating cuts, as might be expected, prolong the time of contraction-waves in their passage through the tissue in which the cuts are interposed. For example, in a spiral strip measuring twenty-six inches in length, the time required for the passage of a contraction-wave from one end to the other is represented by the line _a_ _b_ in the annexed woodcut. But after twenty interdigitating cuts had been interposed, ten on each side of the strip, the time increased to _c_ _d_, the line _e_ _f_ representing one second. And more severe forms of section are, of course, attended with a still more retarding influence. [Illustration: Fig. 15.] The effects of temperature on the rate of contraction-waves are very striking. For instance, in a rather narrow strip measuring twenty-eight inches long and one and a half inches wide, the following variations in rate occurred:-- -------------------------+------------------------------- Temperature of water. | Time occupied in passage of | contractile waves. -------------------------+------------------------------- 26° | 4 seconds. 32° | 3 seconds. 42° | 2-2/5 seconds. 65° | 2 seconds. 75° | 1-3/5 seconds. 85° | Blocked. Or, adopting again the graphic method of statement, these variations may be represented as follows:-- [Illustration: Fig. 16. 26°...... 32°...... 42°...... 65°...... 75°...... 85°...... One second ...] Submitting a contractile strip to slight strains has also the effect of retarding the rate of the waves while they pass through the portions of the strip which have been submitted to strain. The method of straining which I adopted was to pass my finger below the strip, and then, by raising my hand, to bring a portion of the strip slightly above the level of the water. The irritable or contractile surface was kept uppermost, and therefore suffered a gentle strain; for the weight of the tissue on either side of the finger made the upper surface somewhat convex. By passing the finger all the way along the strip in this way, the latter might be gently strained throughout its entire length, the degree of straining being determined by the height out of the water to which the tissue was raised. Of course, if the strip is too greatly strained, the contraction-waves become blocked altogether, as described above; but shortly before this degree of straining was reached, I could generally observe that the rate of the waves was diminished. To give one instance, a contractile strip measuring twenty-two inches had the rate of its waves taken before and after straining of the kind described. The result was as follows:-- [Illustration: Fig. 17. Before straining ... After straining ... One second ... ]