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 slightest indication of the trephine opening appeared.  To take, therefore, a skiagraph of a brain through two thicknesses of skull, with our present methods, is an impossibility.  Even should the difficulty be overcome, it is very doubtful whether there would be any possibility of discovering diseases of the brain, since diseased tissues, such as cancer, sarcoma, etc., are probably as permeable to the X rays as the normal tissues.  Thus Reid ("British Medical Journal,” February 15, 1896) states that a cancerous liver showed no difference in permeability to the rays through its cancerous and its normal portions.

Foreign bodies, such as bullets, etc., in the brain may be discovered when our processes have become perfected.  Figure 7 shows two buck-shot skiagraphed inside of a baby’s skull, and therefore through two thicknesses of bone.  It must be remembered, however, that not only are the bones of a baby’s skull much less thick than those of an adult’s skull, but they are much less densely ossified, and so throw far less of a shadow.