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BULLETIN OF THE BUREAU OF FISHERIES 
The average values for the ash of the blood — that is, the inorganic constituents — 
of the four species of fresh-water mussels examined, were 0.1539 per cent of the weight 
of the blood, or a little more than one-third of the weight of the total solids. Because 
of the low values of the total solids the average per cent of ash in the blood of fresh- 
water mussels is of course much below the ash content of the blood of the vertebrates 
or of most invertebrates. 
The ratio of ash to total solids in the blood, which is an expression of the relative 
amount of organic substances in the blood, varies widely in the several groups of 
animals. (See Table 4.) As the total solids of the fresh-water mussel blood are 
much lower than those of other bloods, the actual per cent of organic solids in the 
blood of the fresh- water mussels is of necessity also much lower than that of other 
bloods. Considering the relative amount of organic constituents, however, the 
fresh-water mussel blood falls about midway between vertebrate serum or plasma 
on the one hand and vertebrate whole blood on the other; that is, the fresh-water 
mussels are near the middle of the invertebrate group when this organic-inorganic 
solids ratio is considered. 
The low total solids and the moderately high ratio of ash to total solids in the 
blood of the fresh-water mussels show this blood to be a very watery fluid, in which 
the low specific gravity indicates a small quantity of solids in solution or suspension 
rather than a mixture containing salts, in amounts comparable to those found in the 
blood of other animals, together with sufficient other substances lighter than water 
to produce the low specific gravity as found. 
BLOOD SUGAR 
Blood sugar, the only organic constituent of the blood considered separately, 
was determined by the Hagedorn- Jensen (1923) iodine titration method for 10 species 
of fresh-water mussels. (See Table 5.) The blood sugar averaged 31 milligrams per 
100 cubic centimeters of blood, in these species, ranging from 7 to 93 milligrams per 
100 cubic centimeters of blood. The average value and the range of variation are 
much the same as those for many other invertebrates, both marine and fresh water, 
in spite of the fact that the total solids and the inorganic salts are much lower in 
fresh-water mussel blood than in other invertebrates. Considering these 10 species 
of fresh-water mussels separately the variation between species was not considered 
significant as it was no greater than that between individuals of the same species in 
several cases. This wide variation in blood-sugar levels between individuals of the 
same species is perhaps the most striking feature in Table 5, but it is not without its 
parallel in other species of mollusks. Lang and Macleod (1920) report the blood 
sugar of the marine clam Schizothaerus nuttali as from 1.5 to 1.8 milligrams per 100 
cubic centimeters, and Myers (1920) found 74 milligrams of blood sugar per 100 
cubic centimeters in the same species; and according to the observations of Couvreur 
and Bellion (1907, 1908) and Sellier (1907, 1908), the amount and the type of sugar 
in the blood of the snail Helix pomatia , varies with the state of activity of the animal. 
It seems, therefore, that the blood sugar values of the fresh-water mussels do not 
differ materially either in average or in range from those of other mollusca, even 
though the blood of the fresh-water mussels is very dilute. 
