The idea was so startling that I could scarcely realise what he meant at first.  I had read of the wonderful work of the surgeons of the Rockefeller Institute in transplanting tissues and even whole organs, in grafting skin and in keeping muscles artificially alive for days under proper conditions.  Could it be that a man had deliberately amputated his fingers and grafted on new ones?  Was the stake sufficient for such a game?  Surely there must be some scars left after such grafting.  I picked up the various sets of prints.  It was true that the third set was not very clear, but there certainly were no scars there.

“Though there is no natural changeability of finger-prints,” pursued Kennedy, “such changes can be induced, as Dr. Paul Prager of Vienna has shown, by acids and other reagents, by grafting and by injuries.  Now, is there any method by which lost finger-tips can be restored?  I know of one case where the end of a finger was taken off and only one-sixteenth inch of the nail was left.  The doctor incised the edges of the granulating surface and then led the granulations on by what is known in the medical profession as the ‘sponge graft.’  He grew a new finger-tip.

“The sponge graft consists in using portions of a fine Turkish surgical sponge, such I have here.  I found these pieces in a desk at Riverwood.  The patient is anaesthetised.  An incision is made from side to side in the stump of the finger and flaps of skin are sliced off and turned up for the new end of the finger to develop in—­a sort of shell of living skin.  Inside this, the sponge is placed, not a large piece, but a very thin piece sliced off and cut to the shape of the finger-stump.  It is perfectly sterilised in water and washed in green soap after all the stony particles are removed by hydrochloric acid.  Then the finger is bound up and kept moist with normal salt solution.

“The result is that the end of the finger, instead of healing over, grows into the fine meshes of the pieces of sponge, by capillary attraction.  Of course even this would heal in a few days, but the doctor does not let it heal.  In three days he pulls the sponge off gently.  The end of the finger has grown up just a fraction of an inch.  Then a new thin layer of sponge is added.  Day after day this process is repeated, each time the finger growing a little more.  A new nail develops if any of the matrix is left, and I suppose a clever surgeon by grafting up pieces of epidermis could produce on such a stump very passable finger-prints.”

No one of us said anything, but Kennedy seemed to realise the thought in our minds and proceeded to elaborate the method.

“It is known as the ‘education sponge method,’ and was first described by Dr. D. J. Hamilton, of Edinburgh, in 1881.  It has frequently been used in America since then.  The sponge really acts in a mechanical manner to support the new finger-tissue that is developed.  The meshes are filled in by growing tissue, and as it grows the tissue absorbs part of the sponge, which is itself an animal tissue and acts like catgut.  Part of it is also thrown off.  In fact, the sponge imitates what happens naturally in the porous network of a regular blood-clot.  It educates the tissue to grow, stimulates it—­new blood-vessels and nerves as well as flesh.