IO4 RALPH S. LILLIE AND WARE CATTELL. 



containing sea-water; these were kept covered except at times of 

 examination, and the sea-water was changed several times. 

 With small numbers of eggs this method is satisfactory and 

 convenient. In each experiment the temperature of the sea- 

 water in the rectangular dish was recorded at the end of. the 

 longest exposure. The temperature was measured by a ther- 

 mometer with the bulb placed near the eggs. A difficulty with 

 this method is that the bulb was incompletely immersed when the 

 layer of sea- water was shallow, as in most of our experiments; 

 this was especially true of the earlier experiments, where the 

 readings were too low and a correction of I to 3 degrees was found 

 necessary; with later experiments a small thermometer with a 

 short bulb was used which gave reliable readings. 



A large number of experiments (more than 50) were performed 

 in which the vessel containing the eggs was immersed in ice water 

 as described above; the current densities used ranged from less 

 than 100 to 318 ma. /cm. The general results of these experi- 

 ments may be summarized as follows. 



With currents of densities ranging from 136 to 242 ma. /cm., 

 flowing from 2 to 12 minutes, activation was either absent or 

 negligible, provided the temperature remained below 29. In all 

 cases where the temperature rose to 30 or higher a variable 

 degree of activation, usually incomplete, was obtained; and in 

 some cases a considerable proportion of eggs developed to the 

 swimming blastula stage. In the experiment showing the most 

 striking effect of this kind (Aug. 22, 1922) a very typical picture 

 of heat activation was presented; after 4 minutes exposure to a 

 current of 227 ma. /cm., only a few eggs (ca. 3 per cent.) formed 

 membranes; with exposures of 8 and 12 minutes almost all 

 formed membranes and a large proportion formed blastulae (ca. 75 

 per cent, with 8 minutes and 25 per cent, with 12 minutes). The 

 temperature at the end of the maximum period of exposure 

 (12 m.), allowing for the error of measurement, was 30 or over. 

 In such a case the activation caused by the current is mainly if not 

 entirely an effect of the high temperature, and not of the current 

 as such. This is shown by the fact that activation was never 

 produced by the same current at lower temperatures (28 or 

 ower) ; also by control experiments in \vhich eggs were activated 



