528 
BULLETIN OF THE BUREAU OF FISHERIES 
ing difference in tonicity between the blood and the fluid surrounding the animal 
much less. The specific gravity of the blood was definitely reduced during the first 
24 hours of exposure to distilled water and remained low throughout the tests (nearly 
200 hours in some cases). The rapidity of these changes in specific gravity of the 
blood suggests that the osmotic barrier between the blood of the fresh-water mussels 
and the fluid of their environment is not great, the fluid of the body tending to come 
to equilibrium with the environment rather promptly. The pH value of the blood 
was maintained fairly weii as long- as the animal was reasonably active, but the 
alkalinity of the blood fell as the mussel became moribund or as the exposure to 
distilled water lengthened. 
SODIUM SALTS 
As the fresh-water mussels are supposed to have evolved from marine clams and 
as sodium chloride is the major inorganic salt found in all living animals, sodium 
chloride was chosen as the standard with which to compare the action of the various 
hypertonic solutions used. Besides, as this salt passes through animal membranes 
easily under most conditions, the toxic action of sodium chloride to living tissues, in 
concentrations greater than the so-called physiological solutions, is well known. 
Three solutions of sodium chloride were used in the tests on fresh-water mussels: 
A 0.25 per cent solution, which is roughly isotonic with the blood of fresh-water 
mussels; a 0.50 per cent solution, comparable with the blood of most cold-blooded 
vertebrates, and that of many invertebrates; and a 1.00 per cent solution, which is 
slightly more concentrated than mammalian or avian blood. The data from these 
series of tests are presented in Table 13 and Figure 10. 
Table 13. — Changes in specific gravity and pH of the blood of fresh-water mussels in solutions of sodium 
salts. 
SODIUM CHLORIDE, 1.00 PER CENT 
Scientific name 
Common name 
Hours of 
exposure 
Condition of animal 
pH 
Specific 
gravity 
Washboard 
4 
Heart beating 
8. 0 
1 0046 
do . 
4 
do 
7. 3 
1. 0051 
_do 
4 
do 
7. 6 
1. 0051 
Po 
4 
1. 0051 
12 
7.4 
1. 0056 
do - 
12 
do 
7.4 
1 0072 
Pfl 
12 
7.5 
1. 0073 
24 
7.0 
1. 0053 
SODIUM CHLORIDE, 0.50 PER CENT 
Washboard--. - 
4 
Heart beating 
7.9 
1. 0033 
1.0036 
4 
7.8 
do 
4 
do 
7.8 
do 
12 
do 
7. 5 
1.0054 
1. 0054 
1. 0059 
1. 0049 
_do 
12 
do __ 
7. 8 
do 
12 
. do 
7.8 
24 
Moribund. 
7.0 
__ do. -. . - 
24 
do 
7.0 
1. 0050 
1. 0050 
1. 0050 
_ ...do --- 
24 
Heart beating.. 
7.0 
24 
do 
7.5 
SODIUM CHLORIDE, 0.25 PER CENT 
Washboard . 
4 
Heart beating 
8. 0 
1. 0029 
1. 0036 
1. 0030 
1. 0030 
1.0032 
1.0041 
1.0034 
1. 0034 
do 
4 
do 
8. 1 
. ...do 
24 
7. 2 
24 
7.9 
do 
24 
do 
7.9 
do 
24 
do 
8. 0 
do 
76 
do., 
7. 7 
76 
7.9 
. .--do --- --- 
76 
do 
7.9 
1.0036 
1.0037 
do 
76 
do 
7.7 
NoTE Moribund, ” under condition of animal, designates a mussel in which the heart was not beating when shell was 
opened, but an animal still responding to tactile stimulation of the foot or mantle. 
