Effect of Different Temperatures on the Medusa Cassiopea. 33 



If returned to sea- water at 29 from 44, the nerves may partially 

 recover at first, but later lose their power of conduction, while the 

 muscles can still contract when stimulated by induced shocks. On 

 returning to sea-water at 29 from 44.5 neither the nerves nor muscles 

 recover. The strips eventually disintegrated. The heat stand-still of 

 the sense-organs is also reversible until 44, above which there is no 

 way of telling whether recovery would occur or not. 



At 39.5 the muscles are perfectly relaxed. Although unable to 

 contract they do not pass into heat rigor. On still further raising the 

 temperature the muscles remain in the same relaxed condition until 

 about 55, when they slowly contract. A large amount of whitish slime 

 is given off during the heating. If this temperature corresponds to that 

 of heat rigor in other animals it is exceptionally high. In skeletal 

 muscles of the frog heat rigor occurs at 39, in the mammal at 47, and 

 in the heart of Limulus at 48.5. 



If the tissues of Cassiopea are kept near their temperature limit for 

 longer times, both contraction and conduction stop at lower tempera- 

 tures. The upper temperature limit is therefore a function of time. 

 In this connection two very interesting recent papers may be mentioned: 



A. Meyer 1 has shown that the killing time for bacteria above the 

 temperature at which life continues indefinitely may be calculated from 

 the following equation: 



x = aq n ~* 

 where 



x = time of exposure 



q a constant for a given bacterium 



a = the killing time at 80 C., the first of a series of terms 10 apart 



(80, 90, 100, etc.). 

 w = the term in the series (8o = ist term, 9o = 2d term, etc. For 



1 00 n i = 3 i ) . 



Calculated as Q 10 , the temperature coefficient ~ is 5 for Bacillus 

 subtilis and 4 for Bacillus robur. The reader is referred to the original 

 paper for the values of q and a, which vary with each bacterium. 



Loeb 3 has studied the temperature coefficient for the length of life of 

 sea-urchin eggs at temperatures above normal. If the length of life for 

 T degrees is known and is represented by D, then the length of life for a 

 temperature T n degrees is 2 H D. Q w was found to be about 1000. 

 This is true for the unfertilized as well as the fertilized eggs. In both of 

 these cases it will be seen that Q w is constant for all 10 intervals. I 

 mention them especially because there is another class of vital tempera- 

 ture coefficients in which Q 10 varies according to the 10 interval. I shall 

 speak of this and its meaning later. 



It may be of interest to compare the temperature limits of activity 

 of a tropical animal with those of a northern form. As the analogy 



1 Meyer, A., Berichte; d. deutsch. Bot. Gesell., xxiv, p. 340, 1906. 



2 Qio is the ratio of a constant at T + 10 degrees to a constant at T degrees C., 



or = 



3 Loeb, J., Arch. f. d. ges. Physiol., 124, p. 417, 1908. 

 3 



