BLOOD OF FRESH-WATER MUSSELS 
529 
The almost immediate rise in specific gravity of the blood of fresh-water mussels 
when placed in these solutions of sodium chloride is in sharp contrast with the results 
of the distilled water series, and confirms the statement made in the discussion of the 
distilled water series that the restriction to osmotic adjustment between the blood 
of the fresh-water mussel and its fluid environment is slight. Within four hours 
after placing the mussels in these salt solutions the specific gravity of the blood of 
all individuals exceeded the average normal specific gravity for the blood of fresh- 
water mussels excepting one. This mussel (see fig. 10) was placed in 0.50 per cent 
sodium chloride solution while closed, and without a cork between the valves. It is 
probable that very little of the salt solution 
penetrated to the soft parts of this animal 
as it was not observed to open its valves 
during this 4-hour period. Several other 
mussels were tested in the salt solutions in 
this same way; that is, they were closed 
in air and then placed in the solution while 
closed without cork between the valves. 
The data from these animals have been 
included in Figure 10 (not in Table 13) for 
comparison. For the most part these 
closed animals remained closed in the salt 
solutions and took little of the test solu- 
tions inside their shells, as the blood specific 
gravities attest. 
By graded additions of salt to the 
water in which European fresh-water mus- 
sels (Anodonta and Unio) were living, Beu- 
dant (1816), found that these animals could 
adapt themselves to almost 2 per cent salt 
solution. Similarly, Philippson, Hanne- 
vart, and Thieren (1910) were able to 
raise the salt content of the water in which 
specimens of the European fresh-water 
mussel, Anodonta cyynea, were living to 
2 per cent if sodium chloride were used, 
or even higher if “sea salt” were added 
gradually. In this work they found, using the electroconductivity method, that the 
salt content of the blood of these fresh-water mussels rose, but that the salt value 
of the blood never equaled the salt content of the surrounding medium, presumably 
because of the presence of some colloidal material in the mussel blood. The return 
of salt-adapted mussels to fresh water was also followed by a drop in the salt content 
of the mussel blood as these animals readapted themselves to the fresh water. These 
observations on the European fresh-water mussel parallel the findings in the present 
series of North American fresh-water mussels. 
The degree of adaptation which North American fresh-water mussels can make 
to solutions of sodium chloride, following the gradual addition of this compound to 
the water in which these mussels are found, is not to be discussed here; but the rapid 
changes in specific gravity of the blood of these mussels following abrupt changes 
1.0070 
1.0060 
1.0050 
1.0040 
1.0030 
1.0026 
1.0020 
1.0010 
1 . 0000 . 
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1 
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i 
4 
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i 
24 
72 
36 
48 
HOURS 
Figure 10. — Specific gravity of the Wood of fresh-water 
mussels in tap water plus sodium chloride. Black circle, 
1 per cent sodium chloride, valves propped open; scored 
black circle, 1 per cent sodium chloride, animal unre- 
stricted; circle, 0.5 per cent sodium chloride, valves propped 
open; scored circle, 0.5 per cent sodium chloride, animal 
unrestricted; black triangle, 0.25 per cent sodium chloride, 
valves propped open 
