tacle to the
passage of the rays, and the shadow originally cast becomes obliterated.
Hence, skiagraphs of the same object exposed to the rays for varying
times may be of value in showing the different tissues. The most
permeable of the normal tissues are cartilage or gristle, and fat. A
kidney (out of the body) is stated by Dr. Reid of Dundee to show the
difference between the rind, or secreting portion, which is more
transparent, and the central portion, consisting chiefly of conducting
tubes, which is less transparent. On the contrary, in the brain the gray
cortex, or rind, is less transparent than the white nerve tubules in the
centre.

The denser fibrous tissues, such as the ligaments of joints and the
tendons or sinews of muscles, cast very perceptible shadows, so that
when we come to a thick tendon like the tendo Achillis, the shadow
approaches even the density of the shadow cast by bone. I presume that
it is for the same reason (the dense fibrous envelope, or sclerotic
coat) that the eye-ball is not translucent to the rays, as is seen in
Figure 5, of a bullock's eye.

[Illustration: FIGURE 5.--SKIAGRAPH OF A BULLOCK'S EYE.

(From the "American Journal of the Medical Sciences," March 1896.)]

Mr. Arthur H. Lea has ingeniously suggested that the translucency of the
soft parts of the living and of those of the dead body might show a
difference, and that, if such were the case, it might be used as a
definite test of death. Unfortunately Figure 6, of a dead hand, when
contrasted with Figure 11, of a living hand, shows virtually no
difference, and the method cannot be used as a positive proof of death.

That we are not able at present to skiagraph the soft parts of the body,
does not imply that we shall not be able to do it hereafter; and should
this be possible, especially with our increasing ability to penetrate
thick masses of tissue, it is evident, without entering into details,
that the use of the X rays may be of immense importance in obstetrics.

The bones, however, as is seen in nearly all of the skiagraphs
illustrating this paper, cast well-defined shadows. This is at once an
advantage and a hindrance. To illustrate the latter first, even one
thickness of bone is difficult to penetrate, so that the attempt to
skiagraph the opening which had been made in a skull of a living person
by a trephine entirely failed, since the bone upon the opposite side of
the skull formed so dense an obstacle that not the sl