160 The Collection of Fishes 
the same manner, but the skin can be rolled up over the head; 
such skins can also be preserved in spirits, in which case the 
traveler may save to himself the trouble of cleaning the head. 
‘‘Some sharks are known to attain to a length of thirty feet, 
and some rays to a width of twenty feet. The preservation of 
such gigantic specimens is much to be recommended, and 
although the difficulties of preserving fishes increase with their 
size, the operation is facilitated, because the skins of all sharks 
and rays can easily be preserved in salt and strong brine. 
Sharks are skinned much in the same way as ordinary fishes. 
In rays an incision is made not only from the snout to the end 
of the fleshy part of the tail, but also a second across the widest 
part of the body. When the skin is removed from the fish, 
it is placed into a cask with strong brine mixed with alum, 
the head occupying the upper part of the cask; this is necessary, 
because this part is most likely to show signs of decomposition, 
and therefore most requires supervision. When the preserving 
fluid has become decidedly weaker from the extracted blood 
and water, it is thrown away and replaced by fresh brine. After 
a week’s or fortnight’s soaking the skin is taken out of the cask 
to allow the fluid to drain off; its inner side is covered with a 
thin layer of salt, and after being rolled up (the head being 
inside) it is packed in a cask the bottom of which is covered 
with salt; all the interstices and the top are likewise filled with 
salt. The cask must be perfectly water-tight.” 
Value of Formalin.—In the field it is much better to use 
formalin (formaldehyde) in preference to alcohol. This is an 
antiseptic fluid dissolved in water, and it at once arrests decay, 
leaving the specimen as though preserved in water. If left 
too long in formalin fishes swell, the bones are softened, and 
the specimens become brittle or even worthless. But for ordi- 
nary purposes (except use as skeleton) no harm arises from two 
or three months’ saturation in formalin. The commercial 
formalin can be mixed with about twenty parts of water. On 
the whole it is better to have the solution too weak rather than 
too strong. Too much formalin makes the specimens stiff, 
swollen, and intractable, besides too soon destroying the color. 
Formalin has the advantage, in collecting, of cheapness 
and of ease in transportation, as a single small bottle will make 
