CARBON DIOXIDE AS A NARCOTIC AGENT. 



455 



in CO 2 as compared with solutions I and 4. The first cleavage 

 appeared as shown in Fig. I, where it will be seen that the shortest 

 cleavage time occurred with the sea water control, represented by 

 Curve i. A lowering of the oxygen tension to slightly over one 

 tenth of the normal value retarded the cleavage time but 4 minutes 



PER 



CENT 



100 



75 



5O 



_L 



30 



6O 



90 



120 



15O 



MIN. 



FIG. i. The relative effectiveness of low oxygen tensions and high CO 2 

 tensions in delaying the first cleavage of Arbacia eggs. Exposures were 

 of thirty minutes' duration. Temperature, 19.8 -20.2. Abscissa = time, 

 in minutes, after insemination. Ordinate = percentage of eggs showing 

 the first cleavage. 



Symbol. 



Curve i O Circles 



Curve 2 X Crosses 



Curce 3 Dots 



Curve 4 A Triangles 



cc. Oxygen. 



per Liter. 



5-15 

 5.56 

 1.26 

 0-55 



C02. 



60% 

 60% 



(Curve 4). On the other hand, an increase of the CO 2 content 

 to give pH of 5.3 was sufficiently great to retard the cleavage time 

 36 minutes, irrespective of the oxygen present, since a single curve 

 serves to represent cleavage in the two solutions which, although 

 showing more than a 4: i difference in oxygen content, had the 

 same carbon dioxide content. Since from such experiments as 



