Effect of Different Temperatures on the Medusa Cassiopea. 31 



So much for a vindication of the experimental method. As for the 

 results, they have been in part stated in my preliminary report. 1 Using 

 the sense-organs as the source of stimulus and a temperature interval 

 of 24 to 34 C. 2 there is without doubt a very marked increased efficiency 

 of both MgCl 2 and CH 3 COOH in stopping both contraction and conduc- 

 tion at the higher temperature (34). At 34 functioning ceases 2 to 2.5 

 times as soon as at 24. This value is identical with van't Hoff's coeffi- 

 cient (2 to 3) for increase in velocity of chemical reactions with 10 rise 

 of temperature. 



Inasmuch as a similar value was not obtained with 20 to 30 as 

 the 10 interval, and the stimulus given out by the sense-organs may 

 have varied in strength at different temperatures, it has seemed better 

 not to publish any data until further experiments can be made. It is 

 hoped that they will afford sufficient evidence to decide the question. 



TEMPERATURE LIMITS OF ACTIVITY AND THERMAL DEATH-POINTS 



OF MUSCLE AND NERVE. 



METHOD. 



The muscles and nerves of Cassiopea form a layer almost as thin as 

 paper over the whole of the subumbrella surface, the nerves outermost. 

 Although intimately connected and impossible to separate by dissec- 

 tion, the greater resistance of the nerves to temperature extremes 

 renders possible a study of their properties apart from the muscles. 

 This is done in the following way, first described by Mayer 3 in studying 

 the effects of salts. A long strip of disk-tissue with several sense-organs 

 on one end is laid across three dishes filled with sea-water (A, B, and c, 

 fig. i). 



FIG. i. 



Stimuli are constantly arising in the sense-organs in dish A, and pass 

 along the strip of tissue stimulating the muscles as they go. By slowly 

 raising or lowering the temperature of the sea -water in B, a temperature 

 can be found where contraction of the muscles ceases, yet the impulse is 

 still transmitted. A cessation of nerve 4 conduction is indicated by the 

 muscles in c, which can then no longer contract, except, of course, on 

 direct stimulation. 



Carnegie Institution of Washington, Year Book, No. 8, p. 117, 1909. 



2 5 either side of the average summer temperature of the water at Tortugas. 



3 Mayer, A. G., Carnegie Institution of Washington, Pub. No. 102, p. 128. 



4 Conduction is assumed to take place always through the nervous network, 

 inasmuch as it has not been shown for Cassiopea that conduction can take place 

 through muscles independently of nerves. 



