110 THE HAUNTS OF LIFE 
It has happened repeatedly that a closed 
glass thermometer sent down inside a metal 
tube has been brought up again powdered to 
a fine dust. In one experiment made on board 
the Challenger, a thick glass tube full of air 
was sealed at both ends, wrapped in flannel, 
and put inside a copper tube with holes at 
each end. This was lowered to a depth of 
2000 fathoms, and was then drawn up again. 
Not only was the glass tube powdered, but 
the side of the copper case was crushed in- 
wards by the pressure. Before the empty 
space caused by the shivering of the glass tube 
could be filled with water, the side of the cop- 
per case was stove in—an “implosion,” as one 
of the explorers said, had occurred. 
Because of the pressure, deep-sea animals 
are “liable to an accident to which no other 
animal in the world is liable—that of tum- 
bling wp.” Most fishes have a silvery swim- 
bladder or air-bladder, which contains gas and 
enables the fish to accommodate itself to dif- 
ferent depths. But this accommodation must 
take place very gradually, and if a deep-sea 
fish, in chasing its prey, rises too high or too 
suddenly, its swim-bladder expands so much 
that it cannot be controlled by the muscles. 
