CARBON DIOXIDE AS A NARCOTIC AGENT. 453 



oxygen per liter. Otherwise, the oxygen content is stated, as is 

 the carbon dioxide content, in terms of percentage saturation. 

 Assuming the applicability of Henry's law to gases in solution, it 

 may be said that when 20 cc. of oxygen-saturated sea water is 

 added to 80 cc. of CO 2 -saturated sea water, the resulting 

 solution contains CO, at 80 per cent, of saturation value and 

 oxygen at 20 per cent, of saturation value. Since in adding the 

 saturated solutions to the eggs they must experience a small in- 

 terchange of gases with the air, a solution which was initially free 

 of oxygen is referred to as having a trace of oxygen, while a CO 2 - 

 saturated solution is represented as having a CO 2 content of 

 "100- ' per cent. Wherever the tension of CO 2 is expressed 

 in mm. Hg the value given is merely an approximate one, calcu- 

 lated for purposes of comparison with the work of other investi- 

 gators on the assumption that the tension of carbon dioxide in a 

 saturated solution is 760 mm., minus the vapor pressure of water 

 at the temperature in question. 



As already mentioned, the reversibility of the effects of CO 2 

 was determined by returning the eggs to sea water for development 

 after the desired periods of exposure. Following a rinsing in sea 

 water, the eggs were placed in small Pyrex beakers containing sea 

 water to a depth of about 1.5 cm. Samples of the eggs were re- 

 moved from the beakers at various times and were preserved for 

 subsequent observation by the addition of a weak solution of 

 formalin in sea water. The fixed eggs were placed in a large 

 hanging drop where, if free from debris, they tended to settle in 

 rows, which simplified the task of determining the percentages of 

 eggs which had undergone the first cleavage. These values, found 

 from time to time after a given exposure, give, when plotted 

 against the minutes after fertilization, a curve which will be re- 

 ferred to as the cleavage curve for that particular exposure. The 

 characteristic S-shape of this curve is related to the variability of 

 the eggs themselves in the manner discussed by Loeb and Northrop 

 (1917) and by Brooks (1918). The time required for cleavage 

 in 50 per cent, of the eggs has in these experiments been used as 

 the most convenient criterion of the cleavage rate, but other per- 

 centages could equally well be compared ; the time in question can, 

 31 



