Another method of seeing the denser tissues of the body is by direct observation.  A means of seeing through the thinner parts of the body, such as the fingers or the toes, has been devised simultaneously by Salvioni of Italy, and Professor Magie of Princeton.  Their instruments are practically identical, consisting of a hollow cylinder a few inches long, one end of which is applied to the eye, the other end, instead of having a lens, being covered by a piece of paper smeared with a phosphorescent salt, the double cyanide of platinum and barium.  When the hand is held before a Crookes tube, and is looked at through the cylinder, we can see the bones of the hand or foot almost as clearly as is shown in Figure 2.  It has not yet, I believe, been applied to thicker parts of the body.  Figures 3 and 4 show a baby’s foot and knee as seen through this tube.  The partial development of the bones accounts for the peculiar appearance.  There is no bony knee-pan, or patella, at birth, and the bones of the toes consist only of cartilage, which is translucent, and therefore not seen.  The name given by Professor Salvioni to this sort of “spy-glass”—­if one may apply this term to an instrument which has no glass—­is that of “cryptoscope” (seeing that which is hidden).  The name suggested by Professor Magie is “skiascope” (seeing a shadow.)

This leads me to say a word in reference to the nomenclature.  The very unfortunate name “shadowgraph” has been suggested and largely used in the newspapers, and even in medical journals.  It has only the merit of clearness as to its meaning to English-speaking persons.  It is, however, an abominable linguistic crime, being an unnatural compound of English and Greek.  “Radiograph” and its derivatives are equally objectionable as compounds of Latin and Greek.  The Greek word for shadow is “skia,” and the proper rendering, therefore, of shadowgraph is “skiagraph,” corresponding to photograph.

The first question that meets us in the use of the method in medicine is what normal constituents of the body are permeable or impermeable to the X rays.  It may be stated, in a general way, that all of the fleshy parts of the body are partially permeable to the rays in a relatively short time; and if the exposure is long enough, they become entirely permeable, so that no shadow is cast.  Even the bones, on prolonged exposure, do not present a sufficient obstacle 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.