518 
BULLETIN OF THE BUREAU OF FISHERIES 
The actual values of sodium chloride in the mussel blood are very low in com- 
parison with the sodium chloride content of the blood of most animals, averaging 
between 0.1 and 0.2 per cent in the fresh-water mussels as against nearly 0.9 per cent 
in the blood of man and the mammals. The sodium chloride values for the blood 
of these North American species of mussels are comparable, however, with the salt 
values computed for the blood of European mussels. Philippson, Hannevart, and 
Thieren (1910) computed the sodium chloride content of the blood of Anodonta 
cygnea on the basis of the electroconductivity, and found it to represent about 0.2 
per cent sodium chloride; and Fredericq (1899) and Monti (1914) give values for the 
depression of the freezing point of the blood of both Unio and Anodonta which would 
approximate 0.2 to 0.3 per cent sodium chloride. 
The average calcium values in the fresh-water mussel blood are about the same 
as those for mammalian blood, in spite of the low salt content of the mussel blood; 
that is, the ratio of calcium to sodium is much higher in mussel blood than in mam- 
malian blood. The maximum calcium per cent in mussel blood greatly exceed the . 
calcium content of mammalian blood. This is not surprising, however, when it is 
considered that the calcium needs of the mussel are large in connection with the 
building and maintenance of a calcareous shell; and Collip (1920) has pointed out 
that, in the case of the marine clam Mya arenaria, the calcium of the shell can be 
used as a buffer to maintain the proper level of the alkalinity in the blood and body 
tissues in the face of various metabolic disturbances. 
By difference the potassium-magnesium fraction was low. This has been con- 
firmed by experimental studies in which it was found that the tissues of the fresh- 
water mussel are quite sensitive to slight changes in the potassium content of the 
medium surrounding them. 
HYDROGEN-ION CONCENTRATION AND BUFFER VALUES 
The pH of the blood of 20 species of fresh-water mussels was determined colori- 
metrically by the Gillaspie (1926) method, brom-thymol blue and cresol red being the 
dyes most frequently employed. Blood for this purpose was taken immediately 
after opening the animal to avoid changes due to loss of carbon dioxide on exposure 
to air. No determinations were made on less than 1 cubic centimeter of blood, and 
the turbidity factor was checked by carrying a control tube of blood behind the stand- 
ard dye tubes in the comparometer block. 
Headings, taken in all months of the year and from both sexes of the various 
species studied (see Table 7), show the blood of the fresh-water mussels to be defi- 
nitely alkaline in reaction and with a more alkaline pH value than that of the blood 
of the higher animals. The average of 142 specimens of fresh-water mussels was 
pH 7.9, the individual readings ranging from pH 7.4 to pH 8.5, with the range pH 
7.6 to pH 8.3 including 94 per cent of the cases. It is difficult to compare the pH 
of the mussel blood with that of man because of several factors, but VanSlyke (1921) 
lists the average pH value for man as 7.4, with a range of pH 7 to pH 7.8 as the limits 
compatible with life. The figures are subject to certain limitations, but greater 
alkalinity of the mussel blood is evident. (See Table 7 and fig. 4.) 
