520 
BULLETIN OF THE BUREAU OF FISHERIES 
This observation is of interest in connection with the fact that the calcium content of 
the mussel blood is high and that the mussel blood is a medium which must transport 
relatively large quantities of calcium in connection with the production of the shell. 
Collip (1920) has stated that in the marine clam, Mya arenaria, the calcium 
carbonate of the shell is available for the animal as an almost unlimited source of 
buffer material, so that the carbon dioxide produced during the activity of the animal 
could unite with the calcium carbonate of the shell, forming a bicarbonate which is 
freely soluble and alkaline in reaction. In the event that the carbon dioxide could 
not be removed promptly from the body of the animal, as during periods when the 
animal is removed from the water or while it has its shell closed tightly even though 
still in the water, the carbon dioxide produced could be buffered down and the alka- 
line value of the blood maintained. This explains the absence of acid values for the 
pH of the blood of fresh-water mussels which were held in air in a closed condition 
for several hours (v. i.). There is evidence (v. i.) that the closed mussels continue 
to use the oxygen in the water contained in the shell when tightly closed, and that 
this buffering out of the carbon dioxide formed during the absence of fresh circulating 
water from the outside by the calcium carbonate of the shell, makes possible the utili- 
zation of the oxygen contained. (See salt experiments.) 
Another check on this point of the buffering value of the shell in the closed 
animals was made by titration of the buffer value of the blood, in terms of N/44 
hydrochloric acid, for mussels just removed from the water and in which the blood 
was presumably well aerated. These values given in Table 8 show that the buffer 
value of the blood is quite low, and as there are only small amounts of proteins and 
other organic buffers in the blood of the fresh-water mussels this buffer value must be 
due very largely to the inorganic carbonates present. It has been noted previously 
in this discussion that the salt-ash content of the blood of the fresh-water mussels 
just removed from the water was lower than that of those animals which had been 
held out of water for some time. Part of this rise in salt content is due to a concen- 
tration of the blood— that is, a water loss; but part of it may also be due to the addi- 
tion of calcium carbonate to the blood, withdrawn from the shell to buffer down the 
carbon dioxide formed. Collip (loc. cit.) found an increase in the calcium content of 
his marine clams under such conditions. 
Table 8. — Buffer values of the blood of fresh-water mussels 
[Cubic centimeters of N/44 hydrochloric acid required to titrate 5 cubic centimeters of blood] 
Scientific name 
Common name 
N/44 hydro- 
chloric acid 
cubic cen- 
timeters 
Scientific name 
Common name 
N/44 hydro- 
chloric acid 
cubic cen- 
timeters 
1. 05 
Actinonais carinata ... 
River mucket 
1. 15 
Do 
do. ... 
1.05 
Do 
do 
1. 20 
Do .. 
1 35 
1.05 
Do 
do. 
1. 35 
1. 03 
Average 
1. 18 
Do 
do 
1. 05 
BLOOD GASES 
As the carbon dioxide of the blood seems so definitely tied up with the salt con- 
tent of the blood, particularly the calcium content, analyses for blood gases were 
made with the Van Slyke apparatus (1917) immediately after the mussels were taken 
from the water. Determinations for oxygen, carbon dioxide, and nitrogen were made, 
