712 ZOOLOGY: L, R, GARY 
measure of the CO2 concentration necessary to bring about narcosis. 
In nearly all instances the activated half disk was the first to succumb, 
and when it had stopped it did not again pulsate until once more stimu- 
lated by an induction shock. The active half disks showed more resist- 
ance to CO2, and when removed from the jars in which they had ceased 
to pulsate and put into fresh sea water would start pulsating again within 
one or two minutes, even when they had been inactive for several hours. 
When the closed jars, in which the medusae were kept for these experi- 
ments, were allowed to remain in the light, the disks would continue to 
pulsate for several days as the CO2 would be in part used up by the sym- 
biotic algae which are very abundant in the tissues of Cassiopea. 
The results of a typical experiment are shown in table 5, in which the 
half disk with sense-organs is designated and the activated half 
disk ''br 
TABLE 3 
No. of Specimens 
a 
b 
a 
b 
Weight 
Pulsation Rate 
in grams 
1.45 p.m. 
4.40 p.m. 
7.30 p.m. 
H' Concentration 
22.8 
44 
62 
18 
7.80 
23.0 
128 
136 
120 
7.90 
30.0 
36 
34 
22 
8.00 
30.5 
88 
86 
98 
8.00 
39.0 
44 
36 
8 
7.90 
41.0 
130 
158 
126 
7.90 
28.00 
56 
22 
25 
7.90 
29.00 
96 
106 
Out 
8.00 
29.25 
84 
32 
32 
7.90 
28.75 
116 
120 
132 
7.90 
The hydrogen ion concentration of the sea water determined at the 
beginning of the experiment was PH. 8.10 (8 X 10"^) so that the change 
brought about in its reaction on account of the activity of the several 
half disks was from 0.1 to 0.3 of the PH. unit. Using the same volume 
(1200 cc.) of fresh sea water, it was found that the addition of the 5 cc. 
of CO2 would usually bring about a change of 0.2 in the PH. reading, so 
that each half disk had apparently given off approximately that volume 
of CO2, in the 8 hours during which they were in the jars. When the 
specimens were left for a longer time in the jars the amount of CO2 
giv^n off became proportionately less as time went on as the disks be- 
came more thoroughly narcotized, so that when the hydrogen ion con- 
centration of the water had become 7.8 the disks had ceased pulsating. 
If left for some hours in this water, the nervous system became incapable 
of transmitting impulses and finally the sense-organs were rendered 
inactive. 
1 Gary, L. R., these Proceedings, 1, No. 12; /. Exper. Zool., 21, No. 1. 
2 Mayer, A. G., Fnhl. Carnegie Inst. Washington, No. 183. 
