94 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
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 strain- 
ing of the kind described. The result was as 
follows :— 
Before straining... 
After straining ... 
One second ... 
Fig. 17. 
Immediately after severe handling of this kind, 
the retardation of contraction-waves is sometimes 
even more marked than here represented; but I 
think this may be partly due to shock, for on 
giving the tissue a little while to recover, the rate 
of the waves becomes slightly increased. 
Anesthetics likewise have the effect of slowing 
the rate of contraction-waves before blocking them. 
Taking, for instance, the case of chloroform, a narrow 
spiral strip between one and two feet long was 
immersed in sea-water containing a large dose of 
the anesthetic; the observations being taken at six 
seconds’ intervals, the following were the results :— 
