BLOOD OF FRESH-WATER MUSSELS 
521 
and the results are tabulated in Table 9. As might be expected of a blood without 
pigmented, oxygen-carrying corpuscles, and with a very low total solids content, the 
volume of blood gas was small. When compared with the blood of marine bivalves 
(Cuenot, 1901; Winterstein, 1909), the oxygen and nitrogen values of the blood of 
the fresh-water mussels and some of the marine clams are found to be much the same, 
but the carbon dioxide content of the blood of the fresh-water mussel is much lower 
than that of the marine clams cited above or of the Japanese oyster, as determined 
by Kokubo (1929). This fact again points to the adjustment of the buffer value and 
the carbon dioxide tension in the blood of the fresh-water mussels, for the blood gas 
determinations listed here for fresh-water mussels’ were Viade as soon as possible after 
the animals were removed from the water. 
Table 9. — Gas content of fresh-water mussel blood 
Scientific name 
Common name 
Total 
gas 
Gases in 100 cc. of blood; that is, volumes per 
cent 
O 2 plus 
CO 2 
O 2 
CO 2 
N 2 and 
other gases 
Buckhorn 
2.33 
1.08 
0.71 
0. 36 
1. 25 
Ambloma costata _ 
Three-ridge ... . ... 
2.36 
.56 
1.80 
Do 
do. 
1. 86 
.78 
1. 08 
Do 
do 
2.27 
.98 
. 33 
. 65 
1. 29 
Do 
do 
2.09 
.89 
.32 
.57 
1. 21 
Southern floater 
2.23 
.72 
.36 
.36 
1. 51 
Do 
do. __ . 
2.41 
1.07 
.89 
. 18 
1.34 
Yellow sand-shell 
2. 16 
.72 
1. 44 
Do 
do 
2.61 
.99 
1. 62 
Do - 
do ... 
2.06 
.86 
.52 
.34 
1. 20 
Do 
1.72 
.52 
.43 
.09 
1. 20 
Do 
do ... 
2.26 
.89 
. 24 
.65 
1.37 
Do - 
do .. 
2. 12 
.97 
. 16 
.81 
1. 13 
Do 
do . 
1.87 
.72 
.27 
.45 
1. 15 
Do 
. . .do. _ .. _ 
1.95 
.80 
.27 
.53 
1. 15 
2. 40 
1. 00 
1. 40 
River mucket 
1.91 
.32 
. 18 
. 14 
1.59 
Average... 
2. 15 
.82 
.39 
.43 
1. 34 
VERIFICATION OF BLOOD-SALT VALUES BY THE FOOT-STRIP METHOD 
It was observed early in the work that the fresh-water mussel maintains a rather 
constant and rhythmical motion of the free margin of the muscular foot. When the 
foot of the mussel is well filled with blood and extruded between the valves of the 
shell, these movements of the foot are of such magnitude that they are easily visible 
to the naked eye as undulating waves of contraction pass up and down the foot margin. 
By attaching a tiny steel hook to the margin of the foot and connecting the foot to a 
recording lever, by means of this hook and an attached thread a graphic record of 
these movements of the margin of the foot of the mussel was easily obtained. 
Placing a small piece of cork between the valves of the mussel when open, and allow- 
ing the animal to retract its foot with the tiny hook attached, the valves in closing 
on the bit of cork were held open far enough to permit the silk thread connecting the 
hook with the recording lever to move freely and operate the lever. In this way it 
was possible to study the movements of the foot margin when completely retracted 
within the shell as well as when expanded. The hook used was so small and light 
in weight that the animal apparently suffered no inconvenience from the presence 
of the hook, as mussels were kept under observation for days with the hook in place. 
To prevent the mussel from moving away from the connected apparatus, a block 
of beeswax was first attached to a glass rod and then to one valve of the mussel by 
