BLOOD OF FRESH-WATER MUSSELS 
511 
If blood samples were to be taken from a single mussel over a period of days 
the procedure was modified. The outside of the shell was ground away on an emery 
wheel until the portion directly over the pericardial cavity was quite thin. This 
grinding was done little at a time, the mussel being immersed frequently in water to 
prevent heating of the shell. When the shell had been ground to a suitable thinness 
in the region desired a “window” was opened in the shell try means of small bone 
forceps and the pericardium exposed. The mussel did not seem to be greatly dis- 
turbed by this operation, and the heartbeats could be counted readily through the 
pericardium. Using a fine dental needle on a Leur syringe the pericardium was 
punctured and blood drawn directly from the heart. After removing the needle 
the heart continued to beat regularly and animals so prepared were kept alive for a 
period of da} 7 s, although samples of blood were drawn daily or at even shorter intervals. 
GENERAL PHYSICAL PROPERTIES 
The blood of the species of North American fresh-water mussels studied is a 
mobile, limpid, lusterless fluid, clear and colorless when first drawn from the heart or 
sinuses, but soon becoming slightly turbid. Drawn blood does not clot into a solid 
mass, but in from one to five minutes after the blood is removed from the body of the 
mussel, particles of a whitish, opaque coagulum appear, suspended like bits of curd 
in the more watery, uncoagulated fluid. These pieces of coagulum which agglutinate 
to some extent form only a small portion of the total volume. On heating to 50° C. 
or above, the separation of the coagulum proceeds more rapidly and as this albuminous 
precipitate settles to the bottom of the container the supernatant fluid becomes 
clear and sparkling. Dried mussel blood has a very faint, yellowish-brown color, 
which deepens on heating or on prolonged exposure to the air. 
SPECIFIC GRAVITY 
The specific gravity of the blood was determined by the Barbour and Hamilton 
(1926) falling-drop method. As this procedure requires only 0.01 cubic centimeter of 
blood, usually three or more determinations were made each time a sample was taken, 
and the values averaged. 
In Table 1 the summarized data on specific gravity of the blood from 145 indi- 
vidual mussels, representing 19 species, are given. Only animals which appeared to be 
in good condition and which had not been subjected to experimentation were incor- 
porated in this series. The determinations grouped in Table 1 include readings 
made in every month of the year and from both male and female mussels (see Table 
2 for individual data) in order to obtain the average normal limits of variation in 
blood values. 
The average specific gravity was 1.0026 — a very low value for blood when 
compared with the specific gravity of the blood of man, the pigeon, and common 
fresh-water animals (see Table 3). Even the maximum specific gravity given in 
Table 1, 1.0078, and the maximum specific gravity of the blood from any mussel 
under experimental conditions in these studies, 1.0099 (from a moribund specimen 
of Quaarula metaneora; see Table 17), are well below the values commonly recorded 
for the blood specific gravity of animals other than fresli-water mussels. 
