94< JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



the strip in this way, the latter might be gently 

 strained througliout 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 : — 



Befoye 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 paitly due to shock, for on 

 srivino; the tissue a little while to recover, the rate 

 of the waves becomes slightly increased. 



Ansesthetics 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 anaesthetic ; the observations being taken at six 

 seconds' intervals, the following were the results: — 



