514 
BULLETIN OF THE BUREAU OF FISHERIES 
corpuscles have an average specific gravity of 1.0880 (Kruger, 1925), it would seem 
that a fairer comparison for mussel blood would be one with the plasma or serum 
of vertebrates. The average specific gravity values for the serum or plasma of 
various vertebrates lie between 1.0170 and 1.0309 (Kruger, 1925), and the specific 
gravity of the whole blood of the Japanese oyster, Ostrea circumpicta Pillsbury, which 
like the blood of the fresh-water mussels contains no red blood corpuscles, is between 
1.0230 and 1.0280 according to Yazaki (1929). It is evident, therefore, that the low 
specific gravity of the blood of the fresh-water mussels is not due entirely to the 
absence of red blood corpuscles, since the specific gravity of the blood of the oyster 
is essentially the same as that of the serum or plasma of vertebrate blood. 
From the distribution of the individual species in Table 1, and from the experi- 
mental tests (v. i.) the average range or normal variation in the specific gravity of 
the blood of the fresh-water mussels studied seems to lie between 1.0010 and 1.0050, 
a variation of 0.0040 and a deviation of —0.0016 to +0.0024 from the average of 
1.0026. Stebbins and Leake (1927), using the Barbour method, report the diurnal 
variation in the specific gravity of the blood of dogs as 0.0044, of men as 0.0033, and 
of women as 0.0027. The actual variation in the specific gravity of the blood of 
fresh-water mussels is therefore of much the same magnitude as that of dogs and man, 
but the proportional change resulting from this variation is very much greater in the 
case of the mussel blood with an average specific gravity of 1.0026 than in human 
blood with an average specific gravity near 1.0554. 
Although fewer specimens of Unioninx than of Lampsilinx, are included in 
Table 1, the grouping of the individual cases suggest that the Unioninx have blood of 
a slightly higher specific gravity than the Lampsilinx. Averaging the specific 
gravities from these two groups in Table 1 separately, the average specific gravity of 
the blood for all species of Unioninx studied falls between 1.0030 and 1.0040 and 
that for all Lampsilinx between 1.0020 and 1.0030. Differences found in experi- 
mental tests also show this same division of species on the basis of the specific 
gravity of the blood. 
TOTAL SOLIDS AND ASH 
The per cents of total solids and of ash contained in the blood were determined 
for four species of North American fresh-water mussels, the pink heelsplitter, Proptera 
alata (Say); the slop bucket, Anodonta corpulenta Cooper; the Lake Pepin mucket, 
Lampsilis siliquoidea pepinensis Baker; and the heelsplitter, Lasmigona compressa 
(Lea). For each species, the blood from several individuals was collected into a 
weighed pyrex beaker until a sample of 100 cubic centimeters or more was obtained. 
The beakers were then reweighed, and the blood slowly evaporated to dryness at tem- 
peratures below 60° C. The solid residues in the beakers were desiccated at 90°-105° 
C. in an electric drying oven, cooled over sulphuric acid, and weighed. Each residue 
was divided into convenient samples (0.3 to 0.5 gram), which were ignited in a plati- 
num dish at a dull red heat and the ash brought to a constant weight. The per 
cent of total solids and of ash in the blood are given in Table 4. 
