88 POPULAR SCIENCE MONTHLY.
cated. A mixture of formalin and alcohol is favorable to the pre- servation of markings. In the museum all specimens should be removed at once from formalin to alcohol. No substitute for alcohol as a permanent preservative has been found. The spirits derived from wine, grain, or sugar is much preferable to the poisonous methyl or wood-alcohol.
In placing specimens directly in alcohol, care should be taken not to crowd them too much. The fish yields water which dilutes the spirit. For the same reason, spirits too dilute are ineffective. On the other hand, delicates fishes put into very strong alcohol are likely to shrivel, a condition which may prevent an accurate study of their fins or other structures. It is usually necessary to change a fish from the first alcohol used as a bath into stronger alcohol in the course of a few days, the time depending on the closeness with which fishes are packed. In the tropics, fishes in alcohol often require attention within a few hours. In formalin, there is much less difficulty with tropical fishes.
Fishes intended for skeletons should never be placed in formalin. A softening of the bones which prevents future exact studies of the bones is sure to take place. Generally alcohol or other spirits, arrack, brandy, cognac, rum, sake, 'vino' can be tested with a match. If sufficiently concentrated to be ignited, they can be safely used for pre- servation of fishes. The best test is that of the hydrometer. Spirits for permanent use should show on the hydrometer 40 to 60 above proof. Decaying specimens show it by color and smell, and the collector should be alive to their condition. One rotting fish may endanger many others. With alcohol it is necessary to take especial pains to ensure immediate saturation. Deep cuts should be made into the muscles of large fishes as well as into the body cavity. Sometimes a small distilling apparatus is useful to redistil impure or dilute alcohol. The use of formalin avoids this necessity. Small fishes should not be packed with large ones; small bottles are very desirable for their preservation. All spinous or scaly fishes should be so wrapped in cotton muslin as to prevent all friction.
The methods of treating individual groups of fishes and of hand- ling them under different climate and other conditions are matters to be learned by experience. Eternal vigilance is the price of a good collection as it is said to be of some other good things. Mechanical collecting, picking up the thing got without effort and putting it in alcohol without further thought, rarely serves any useful end in science. The best collectors are usually the best naturalists. The collections made by the men who are to study them and who are competent to do so are the ones which most help the progress of ichthyology. The stu- dent of a group of fishes misses half the collection teaches if he has made no part of it himself.