There are two ways to clean the skeletons of large mammals: (1) by boiling the bones, and (2) by maceration. The first is short, cleanly, and agreeable; but the skeleton produced by it is sure to be full of grease, and is anything but white and pleasing to look upon when mounted. The boiling process is also detrimental to the texture of the bone. The professional osteologist, to whom a greasy bone in a mounted skeleton is an unpardonable offence, never thinks of boiling a skeleton to get the flesh off, for the reason that the grease is boiled into the bone instead of out of it. Cleaning by boiling is permissible only under exceptional circumstances. If you wish a particular skeleton for a special purpose within a very short time, or if you are so situated that macerating a skeleton is impossible then boiling is excusable, but steaming is far preferable.

Preparing a Skeleton for Maceration.—It is, of course, to be understood that it is only the skeletons that are too large to be scraped and mounted as "ligamentous skeletons" that are to be macerated, bleached, and afterward articulated with wire. The first thing to do is to cut out the sternum in one piece, as already shown in Plate XXI., poison it in arsenic water, and hang it away to dry and be scraped afterward. A sternum must never be macerated, for it is so soft the cartilaginous framework would be entirely destroyed. The skeleton must now be cut completely to pieces, excepting that it is not necessary to separate all the vertebrÆ of the spinal column. The ribs must be cut off, and the joints of the legs cut asunder. The large bones of the legs contain marrow, and of these bones each one must have a large hole drilled in each end on the face of the articulating surface, so that when mounted the holes will not show. These holes are to afford the water access to the interior of the bone.

Macerating and Cleaning.—The maceration of a skeleton is a question of time as compared with eternity. Procure a wooden barrel or keg large enough to contain the entire skeleton, knock the head out and see that there are no nails, nor any other metal anywhere on the inside to stain and discolor the bones. Pack the skeleton closely in the empty barrel, fill it up with water and let it stand. In a few days its offence, like Othello's, "is rank, and smells to heaven." But that is no matter, provided your barrel has no neighbors. Let it stand for four months, six months, a year, or two years if need be, until every particle of fleshy matter on the bones has disintegrated and become a pulp. Keep the barrel covered, and when the water evaporates and the bones on top are about to be exposed, fill up with water and keep the bones always covered. If a skeleton is very bloody, it is well to soak it for a week in salt water to dissolve the blood-corpuscles. Then it may be macerated as directed above. The odor will be horrible, but if you are going to study bones you must not mind that.

When you find upon examining the bones that the flesh has totally disappeared from them, leaving them dark-colored or even black, but without any fleshy matter upon them, they are then to be taken out. Pour off the water, place the entire contents of the barrel in a large sieve-bottomed tray, and wash the bones thoroughly. When that has been done, put them in a large tub of boiling water, and keep them in warm water while you scrape all the bones, one by one, with your bone-scraper, and scrub them with a stiff brush, going over the entire surface, and washing them meanwhile in the warm water. The interior of each of the large leg bones must be washed out with a strong syringe, and every cavity in the vertebrÆ must be carefully scraped out.

Bleaching.—Having carefully scraped and washed the bones, the entire skeleton is now to be soaked for a short time, the length of time varying according to the size and age of the skeleton, in a solution of chloride of lime and water. To make this of the proper strength, dissolve about two or three ounces of chloride of lime in a barrel of water. Bones of young or immature animals must not be left in this solution as long as those of old specimens. Young bones are soft and porous, and the chloride of lime will soon destroy them if they remain in it too long.

The following skeletons, adult in every case, require to be left in this solution a length of time as stated herewith: Dog, 6 hours; sheep, 6 hours; deer, 8; buffalo, 12; elephant, 12.

After removing the bones from this bath, wash them with clear water, lay them in slat-bottomed trays, with cheese-cloth above the slats, without piling one bone upon another, and expose them a number of days in the hot sun. After they have bleached on the upper side, turn them over. If it does not rain upon them occasionally, they should be sprinkled with water, late in the evening or early in the morning, to hasten the process.

Great care is necessary to keep the tiny carpal, tarsal, and phalangeal bones from getting lost. When the bones are white as chalk, or nearly so, tie the parts of each skeleton in a stout paper bag by itself, label it, and put it away until you are ready to mount it.

The sternum is to be soaked in clear water, with a little washing soda to cut the grease, until it is soft, and then scraped the same as the bones of a ligamentary skeleton, which process will be described in the next chapter.