On the Nervous System of Cassiopea Xamachana. 157 



made by means of titrating the sea-water with n/100 NaOH, using 

 phenolphthalein as an indicator and titrating to the color obtained by 

 adding the same amount of indicator to an equal volume of sea-water 

 taken as a control at the beginning of each experiment. 



In the later experiments the amount of C0 2 given off by each half- 

 disk was determined by ascertaining the P H (minus log hydrogen-ion 

 concentration) of a sample of sea-water taken as a control at the 

 beginning of the experiment, and that from the jar in which the speci- 

 men had been respiring during the experiment. Both specimens 

 involved in an experiment were removed from the jars at the same 

 time, whenever the determinations were to be made or either specimen 

 had ceased pulsating. The volume of C0 2 necessary to bring about a 

 corresponding change in the hydrogen-ion concentration of an equal 

 volume of sea-water (1,200 c.c.) was determined by adding known 

 volumes of C0 2 to that volume of sea-water. 



The results of these determinations are shown in figure 13. This 

 result confirms McClendon, who shows that the C0 2 content of sea- 

 water can be more accurately measured by determining the hydrogen- 

 ion concentration than by a direct determination of the C0 2 . 



When the half -disks were placed in the closed jars the increase in the 

 hydrogen-ion concentration of the sea-water caused at first an increase 

 in their rate of pulsation. This was followed after 3 or 4 hours by a 

 gradual decline in rate until finally both activated and active half- 

 disks had been completely narcotized by the C0 2 which they had 

 themselves given off. The decline of the rate of activated half-disks 

 was very regular and the pulsations became gradually weaker, until 

 scarcely discernible before entirely ceasing. The active specimens, on 

 the contrary, behaved very erratically. Frequently when the pulsation 

 had become very slow, or had even ceased for several minutes, these 

 specimens would suddenly take up rapid pulsation and for a short time 

 their activity would be even greater than when under the influence 

 of the first stimulating effect of the increased hydrogen-ion concentra- 

 tion in the early part of the experiment. 



The activated half-disk was invariably the first to become narcotized, 

 the muscles in these, as in all other experiments involving anesthetics, 

 being less resistant to such agents than the sense-organs. 



The activated specimens, when once their pulsations had ceased, 

 were incapable of again taking up pulsation unless stimulated to 

 activity by artificial means. The active specimens, even after having 

 been quiescent for several hours, would take up pulsation within 2 

 minutes after being put into fresh sea-water. 



When such experiments were carried on in daylight narcosis would 

 not be produced during the first day, because of the reduction of the 

 amount of CO 2 in the water by the photosynthetic activity of the 

 zooxanthellae. 



