The method is simple. Injection of the tissue builder, glycerin, or water, is accomplished by the use of a hypodermic syringe. The hypodermic needle is injected at the joint of the finger up into the tip of the finger, care being used to keep the needle below the skin surface (fig. 391). The solution is injected until the finger "bulbs" are rounded out, after which they are inked and printed.
[Fig. 391]
Occasionally, in stubborn cases, entry of the needle at the joint and injection of the fluid will not completely fill the finger bulb. It may be necessary, therefore, to inject the fluid at other points of the finger such as the extreme tip or sides, until suitable results are achieved (fig. 392). The tissue builder has a distinct advantage over glycerin or water, inasmuch as the builder hardens after a short time and is not lost, whereas glycerin and water sometimes seep out when pressure is applied in printing. To offset seepage at the point where the hypodermic needle is injected, whenever possible, tie a piece of string tightly around the finger just above the point of entry of the needle.
[Fig. 392]
When the tissue builder is purchased, a solvent for cleaning the hypodermic syringe and needle should be acquired, inasmuch as the builder will harden in the syringe and needle.
Those cases in which decomposition in its early stage is present belong in this group also. Frequently, the outer layer of skin has begun to peel from the fingers. A careful examination should be made to determine if the peeling skin is intact or if a part of it has been lost. If the skin is in one piece, an effort should be made to secure prints just as though it were attached normally to the finger. Or, if it is deemed advisable, the skin may be peeled off in one piece, placed over the finger of the operator, and inked and printed as though it were his own finger.
Occasionally the first layer of skin is missing. There remains the dermis or second layer of skin which is also of value for identification purposes. This second layer would be dealt with as though it were the outside skin, using the techniques described above. The ridge detail of the second layer of skin is less pronounced than that of the outer skin, however, and more attention and care are needed in order to obtain suitable impressions.