538 
BULLETIN OF THE BUREAU OF FISHERIES 
NEAR FREEZING 
The use of ice in connection with shipments of mussels has been accepted rather 
generally because the melting ice bathes the mussels continuously in a limited amount 
of water, without the disadvantages of a water shipment. Accordingly 60 mussels 
were packed on ice in perforated containers immediately after the animals were taken 
from the river. The containers were so prepared that no water could accumulate 
under or around the mussels, but they were kept moist by the constantly melting ice. 
Blood samples from these mussels were taken at intervals and the data are presented 
in Table 17 and Figure 14 in conjunction with the data from the other air series. 
During the first 48 hours only those animals which were closed were used for 
samples, and these were found on opening to have lost most of the water which was 
included between the valves at the time the mussels were taken from the river. At 
the end of 72 hours exposure to air on ice, all animals still showing tactile responses 
to stimulation of the foot or mantle were sacrificed for samples. At this time 
practically all of the mussels were gapping slightly and the water from the inside 
of the shell had been lost. 
In this group of animals kept on ice in air for 72 hours a blood specific gravity of 
1.0099 was recorded for a specimen the monkey face, Quadrula metanevra. This 
was the highest blood specific gravity found in any of these studies on the blood of 
fresh-water mussels. All of the individuals surviving the ice treatment for 72 hours 
yielded blood with a specific gravity well above the average blood specific gravity 
for normal mussels, and several records were unusually high. The pH value of the 
blood of these mussels of the ice series was less alkaline than normal, and in the 
main the mussels gave the combined picture of blood concentration and low alka- 
linity which was exhibited by moribund mussels throughout the various tests. 
The ice tests were repeated several times on other series of mussels, and it was 
always noted that as the animal became chilled there was a tendency for the ad- 
ductor muscles to relax slightly. As the muscles relaxed the shells gapped apart 
more or less, and the water included between the valves at the time the animal was 
closed was lost more or less completely. The rise in blood specific gravity in mussels 
exposed to air seemed therefore, in part at least, to be associated with loss of this 
water from between the shells. Once the mussel became so numbed that its valves 
began to gap open, the soft parts of the animal were exposed to the direct action 
of the air, if the water between the valves were lost. There seemed to be no mech- 
anism to maintain the concentration of the blood at the normal level while the soft 
parts lost water to the air. 
To test this interpretation of these results, four large southern floaters, Anodonta 
limneana, were prepared by cutting a window in the shell of each in the region of the 
heart, as described in a previous section. Each mussel was then mounted on its 
side with the uncut valve down, in a glass jar, and water added until the uncut 
valve and the opening between the two valves were submerged. In this way the 
mantle cavity of the mussel was filled with water, but water could not enter the 
shell-window which was above the water level at all times. A thermometer was 
inserted through the window and supported so that the bulb of the thermometer 
remained in the pericardial cavity, registering therefore the temperature of the 
fluid surrounding the heart. The glass vessel was then covered to eliminate dis- 
turbing air currents and to reduce evaporation from the mussel to the minimum, 
