356 REPORT OF THE COMMISSIONER OF FISHERIES. 
the drop and in the splash at the surface, all mortality and symptoms 
of gas could be prevented. From water standing without flow in 
ordinary containers the excess of course finally disappeared, but in the 
large Woods Hole aquaria signs of excess were still evident after seven 
days. <A cylindrical glass hatching jar of about 23 gallons capacity, 
after filling with supersaturated water, required to stand two or three 
days before this water failed to produce an external precipitation on the 
body of a tomeod immersed in it as a test. 
ROLES OF NITROGEN AND OXYGEN IN CAUSATION OF THE DISEASE. 
Some consideration may now be given to the separate réles of the 
two gases nitrogen and oxygen in the disease. A reference to Table 
II, page 373, shows that the gas from the fixed gas lesions, that is, from 
the exophthalmia, from the fin blebs, and particularly from the cham- 
bers of the heart, is very high in nitrogen. 
The sample from the sacs of rainbow-trout fry was taken from 
specimens preserved in formalin and some oxygen may have been lost 
on this account. All the others were from fresh material. 
The samples upon which these figures are based were very small, and 
in obtaining them it was impossible to exclude with certainty all con- 
tamination from atmospheric sources. In each case a part of the small 
percentage of oxygen found certainly came directly from the air. 
The sample from the eyes of scup was most lable to this error. That 
from the hearts of various fishes indicates that the gas which causes 
the fatal embolism in the vessels is almost pure nitrogen, and samples 
from this source more accurately represent the gas as released from 
the blood than those from the external blebs or the tissues about the 
eyes. The one sample of the latter sort obtained was largely from 
scup in which gas had inflated the conjunctiva so that this gas was 
separated from the water only by a very thin transparent membrane, 
through which oxygen from the water may have diffused. Likewise 
all the fin blebs have but a similar osmotic membrane protecting the 
contained gas from changes in its original composition. The heart 
gas, however, doubtless represents solely a direct precipitation from 
the blood. It would appear, then, that it is the nitrogen gas chiefly, 
if not solely, which plays the essential part in the disease. The 
gas from the supersaturated blood is certainly not in pro- 
portions analogous to that of the separation of nitrogen and oxygen 
from water supersaturated with air. In air-saturated water the oxy- 
gen is about 33 per cent of the total oxygen and nitrogen dissolved. 
In water air-supersaturated under the mechanical conditions here 
described the percentage of oxygen dissolved is slightly less, for the 
excess is not taken up in the same proportions that it is from the atmos- 
phere. When unsaturated water is shaken with air at ordinary pres- 
sure, the residue of undissolved gas is richer in nitrogen than the 
separation of 
