540 
BULLETIN OP THE BUREAU OF FISHERIES 
These values collectively show the blood of fresh-water mussels to be very low in 
solids as compared with the blood of other animals, both fresh-water and marine. 
The blood of fresh-water mussels is more alkaline than that of most animals, and 
varies over a rather wide range on the alkaline side of neutrality; in this respect the 
blood of fresh-water mussels being comparable to that of other mollusca as noted by 
Giersback (1891). 
Although the blood of fresh-water mussels was found to contain only very small 
quantities of inorganic salts, it was demonstrated by means of physiological tests on 
living preparations of the foot and of the heart of fresh-water mussels, that these 
salts, even though present in the blood in low concentrations, are essential for the 
life activities of the mussels; and that these salts are balanced against each other as 
in the higher animals. The activity of the heart and of the foot of these fresh-water 
mussels ceased promptly if the proportions or the quantities of these salts in the blood 
were increased or diminished beyond rather narrow limits. 
The fresh-water mussels were found to be very sensitive to changes in the salt 
content of the water in which they were living. When small quantities of common 
salt or various other inorganic salts were added to the surrounding water, the specific 
gravity and salt content of the blood of the mussels changed rapidly in a few hours. 
Similarly if the mussels were transferred from ordinary river water to distilled water, 
the specific gravity and salt content of the blood of the mussels were lowered. From 
these series of tests it was demonstrated that the blood of the fresh-water mussel 
varies with and in the direction of the concentration of the salts in the water in which 
it is living; and as these changes take place rapidly, they suggest that the restriction 
on an osmotic balance between the blood of the mussel and the fluid surrounding the 
mussel is slight. Since the fresh-water mussel is very limited in its locomotion, this 
facile modification of the blood by the environment makes the fresh-water mussel 
particularly susceptible to changes in water composition resulting from the introduc- 
tion of various industrial wastes into the mussel-bearing streams. 
Exposure to air either at ordinary temperatures or on ice, caused the specific 
gravity of the blood of fresh-water mussels to rise, indicating a concentration of the 
blood. This concentration of the blood, which rapidly reached a critical level, was 
accelerated if the mussel lost the water which was retained inside of the shell when 
the animal was removed to the air. As mussels packed on ice were soon so numbed 
that the adductor muscles relaxed sufficient!} 7 to allow the shells to gape open and 
the water to drain out, mussels so packed succumbed more rapidly than those which 
were packed in moist sphagnum or other damp material. 
The alkalinity of the blood was reduced and the specific gravity rose in moribund 
fresh-water mussels. 
The blood can be used as an index of the physiological condition of fresh-water 
mussels. 
BIBLIOGRAPHY 
Abderhalden, E. 
1911. Textbook of physiological chemistry, 722 pp. New York, p. 554. 
Barbour, Henry G., and William F. Hamilton. 
1926. The falling-drop method for determining specific gravity. Journal of Biological Chem- 
istry, Vol. LXIX, 1926, pp. 625-640. Baltimore. 
Beudant, F. S. 
1830. Annales de Chimie et de Physique, Tome 2, 1816 (1830), pp. 32-41. Paris. 
Bottazi, Fil. 
1911. Physikalisch-chemische Untersuchungen des Harns und der anderen Fliissigkeiten. 
In Der Harn usw., by C. Neuberg, Teil II, 1911, pp. 1396-1761. Berlin, p. 1725. 
