BLOOD OF FRESH-WATER MUSSELS 
527 
In Figure 4 a relation between the specific gravity and the pH of the blood of 
fresh-water mussels was pointed out; namety, that as the blood approached neutrality 
the specific gravity rose — that is, the more alkaline bloods were usually those with 
the lower specific gravities. Under both the discussion of blood salts and of blood 
gases it was also noted that during exposures to conditions causing retention of car- 
bon dioxide in the body of the mussel, the animal made more or less compensation 
by buffering down the carbon dioxide with calcium carbonate withdrawn from the 
shell. This addition of calcium salts to the blood, of course, affects the specific 
gravity of that fluid, not only through the actual addition of calcium salts and the 
retention of carbonates in the blood but also through the effects on various other 
constituents of the blood. 
Throughout the several series of experimental tests, both with salts and with 
exposures to air, it was observed that as the mussel became moribund the specific 
gravity of the blood usually rose, and with this rise in specific gravity the pH 
va ] ue of the same blood approached neutrality; that is, became less alkahne. In 
animals which had been moribund or dead for several hours (but before decomposi- 
tion changes set in) the blood frequently became quite alkaline again. This sequence 
of specific gravity and pH changes in the blood of living mussels and those which 
had just died was interpretated as showing the buffering action of the calcium car- 
bonate of the shell on the acid products which are known to form in the tissues of 
moribund animals. It is also possible that changes in permeability develop under 
these conditions. 
Applying these observations to the distilled water cases, the specific gravitj 7 of the 
blood of these mussels might be expected to rise slightly as the animal became mori- 
bund from the effects of the distilled water, but was still tending to buffer down the 
accumulating acid products. 
Three checks were made. Mussels were placed in distilled water pH 5.3, and 
they were found to die more rapidly than mussels in the same distilled water adjusted 
to pH 6.8, particularly if the acid distilled water were changed frequently. If mussels 
were placed in distilled water pH 5.3 the pH of the water rose to pH 6.8 in 24 hours 
whereas control jars without mussels showed no change in pH. In order to evaluate 
this change in pH in the water around the mussels, fresh, empty mussel shells from 
which the living animals had just been removed were wiped dry and the inner surfaces 
completely coated with paraffin; that is only those parts of the shell which would be 
in contact with the water, were the shell occupied by the living mussel, were left 
uncoated with paraffin. The paraffined shells were then placed in acid distilled 
water pH 5.3 and treated as if the shells contained living mussels. After about 30 
hours the pH of the water around these paraffined shells had risen to pH 6.8, where 
it remained. In the third check, mussels were placed in distilled water pH 5.3 and 
no change of fluid made, but the usual aeration was maintained. After 24 hours the 
water around these mussels had a pH of 6.8 and 24 hours later it had risen to pH 7.3. 
The blood of these mussels was near but still below average normal at the end of 
144 hours. The distilled water even under these conditions continued to be toxic, 
and the animals died after about 200 hours. 
Considering all of the distilled water data collectively the fresh-water mussels 
were found to be very sensitive to the hypotonic and unbuffered conditions of the 
environment offered by distilled water, in spite of the fact that the blood of the fresh- 
water mussels is much more dilute than that of the higher animals, and the correspond- 
