18 
THE YOUNG SCIENTIST. 
where a tank of water has become charged 
with a sudden development of minute 
animal or vegetable life, causing the water 
to look cloudy. With the assistance of 
a few mussels the water can be restored 
Fig. 1. UNIO EADIATUS. 
to its original clearness in a few hours. 
It is these minute vegetable and animal 
organisms that constitute the natural 
food of the mussel. On very many occa- 
sions, in the months of Jaly and August 
particularly, when the temperature of the 
water in my tanks was rapidly approach- 
ing 80°, causing immense and sudden de- 
velopments of animal and plant life, I 
Fig. 2. ANADON FLUVIATILIS. 
have used mussels with perfect success. 
Xiike the other animals confined in an 
aquarium, they must be watched, and 
that very closely, for if one sliould hide 
away and die and not be discovered it will 
be very apt to poison the water beyond 
recovery. A dead mussel can be known 
by his gaping shell ; still, when doubtful, 
touch his shell near the syphons with a 
stick, and if he does not close up quickly, 
it is best to take him out and examine 
him carefully 
Thousands of these mussels are taken 
every year for the valuable pearl material, 
of which their shells are mainly composed, 
and which is worked into various articles 
by workers in i)earl both in this country 
and Europe. Large quantities of these 
shells are shipped to England to be 
polished and mounted in gold and silver 
for ladies portemonnaies, which are again 
shipped to this country to be sold, they 
being in great demand by the fair sex, 
yet, if they were told that they were 
carrying in their pockets American clam 
shells, how quickly their admiration 
would cease. 
It is not so many years ago since the 
inhabitants of New Jersey turned out en 
masse to dig mussels in the streams and 
ditches, for the pearls they yielded, many 
of which sold for high prices. I knew 
of some lumbermen from Maine, who, 
during their leisure hours, collected 
pearls from the mussels growing in the 
small streams and rivers near their camp. 
Some of these pearls were very beautiful 
both in shape and colors, being of blue 
and pink tints, for which they obtained 
high prices from our leading jewelers. 
The rivers of Scotland, Ireland, Wales 
and Bavaria, abound in these pearl-bear- 
ing molluscs, and at the present day 
many fresh water pearls of value are 
being worn by the nobility of Europe. 
Linnaeus discovered by actual experi- 
ment that grains of sharp sand introduced 
between the valves of the shell in such a 
way that they rested between the body of 
the animal and the " Mother-of-pearl," or 
nacre, caused in a short time the deposi- 
tion of a coating or crust of pearl on the 
sand grain, which, acting as a nucleus, 
gathered the shielding matter around it, 
and so guarded the delicate tissues, of the 
mollusc from friction and injury. It has 
also been found that by drilling a small 
hole through the x3uter coatings of the 
shell, and leaving the lining untouched 
by the boring instrument, that a pearl 
nodule was formed. This fact has been 
taken advantage of by the Chinese, who, 
introduce small images of their * Josses ' 
into the valves of the pearl oyster, 
which in course of time coats them with 
1 nacre. 
