THE ROENTGEN OR X-RAYS.
GEISSLER TUBES--VACUUM TUBES OF CROOKES, HITTORF AND LENARD--THE
CATHODE RAY--ROENTGEN’S GREAT DISCOVERY IN 1895--X-RAY APPARATUS--
SALVIONI’S CRYPTOSCOPE--EDISON’S FLUOROSCOPE--THE FLUOROMETER--SUN
BURN FROM X-RAYS--USES OF X-RAYS.
The majority of people have been accustomed to regard light as something
to be excluded and controlled by opaque screens just as effectively as
rain is excluded by a tin roof, or cold is kept out by a brick wall. The
shady retreat furnished relief from the garish day to the primitive man,
and the opaque shades and Venetian blinds of modern civilization exclude
the excess of light at our windows. Sunshine and shadow have, in fact,
been correlated conditions to the ordinary observation of man since time
began. The last few years of the Nineteenth Century, however, were to
witness the discovery of a new kind of light ray which, in its behavior,
subverted all previous conception of the nature and action of light. It
was a species of electric light, which we are accustomed to regard as
brilliant, but this light ray was invisible to the eye. It could not be
refracted or bent from its course by a prism or lens, and it was so
subtle, penetrating and insidious, that it could not be barred out like
sunlight, but passed readily through many opaque substances, such as
wood, flesh tissue, paper (even a book of 1,000 pages), as well as some
of the metals. The lighter the weight of the substance, or less its
density, the easier these rays passed through it, or the more
transparent such bodies were to the rays. The heavier metals, like
platinum, gold and lead, were practically opaque, or allowed none of the
rays to pass through them, while the very light metal aluminum was about
as transparent to these rays as was glass to ordinary light, and for
that reason this metal could form window panes for such rays, while
excluding other light. Most organic substances are transparent or
semi-transparent to these rays, and hence such rays readily pass through
the body of an individual, being only intercepted in part by the denser
parts of the anatomy, such as the bones, so that a man in such light no
longer casts a well-defined shadow of his outline, but the shadow
disclosed is that of a skeleton, by virtue of the greater density of the
bones. Any object of higher density, such as a ring upon the finger,
clearly establishes its shadow by virtue of its greater density.
Likewise, any foreign object in the body, such as a bullet from a
gun-shot wound, or a foreign body accidentally swallowed, is perfectly
disclosed and located by the shadow which it casts. As these light rays
have been characterized as invisible, it may be difficult to understand
how invisible rays can cast a visible shadow, and it should be here
stated that when these unseen rays fall upon certain chemical substances
the latter are made to glow with a peculiar fluorescence, and a screen
made of such fluorescing materials will light up where the rays fall
upon it, and remain dark at the points where the rays are intercepted by
a substance opaque to such rays, thus outlining a shadow.
Not only do these light rays in passing through the body tissues
(transparent to them) cast a shadow of the bones or any foreign objects,
but by the application of photography to these shadow pictures a species
of photograph, called a radiograph, or skiagraph, may be taken, and thus
any foreign body, such as a bullet, may be definitely located in the
human body and quickly extracted, without the element of doubt which
beset the old method of diagnosis, which, at best, was only intelligent
guessing. Not only are foreign bodies so located, but the fractures of
the bones may also be accurately observed, studied and adjusted. Stone
in the bladder may be discovered, and the condition and movements of the
heart and lungs ascertained.
This new kind of light ray was discovered November 8, 1895, by Prof. W.
C. Roentgen, of the Royal University of Wurzburg, and was named by him
the “X-Ray,” probably because the letter x in algebraic formula
represents the unknown quantity, and the hitherto unknown and elusive
quality of this light suggested to Prof. Roentgen this appropriate name.
As before stated, a peculiar quality of the X-Rays is that they are not
visible to the eye. A beam of X-Rays, thrown into a dark chamber through
an aluminum window, would produce no illumination whatever in the room,
but such rays would still penetrate the room, and if a fluorescing
screen were placed in their path it would instantly light up. It is not
surprising, therefore, that these subtle rays should have so long eluded
the observation of the scientist.
A brief sketch of the conditions leading up to the discovery of the rays
is necessary to a proper understanding of the same.
[Illustration: FIG. 215.--THE CATHODE RAY.]
Every student of physics remembers the old-time lecture room
experiments in which the Geissler tubes, with their beautiful play of
colored lights, illustrated the action of the electrical discharge from
the glass plate machine or the Ruhmkorff coil, on rarified gaseous
media. Electrical experiments in high vacua by Sir William Crookes, and
by Hittorf and Lenard, have greatly added to the present knowledge in
this field, and paved the way to the discovery of Prof. Roentgen. It was
known that a vacuum tube, variously called after the names of these
scientists, as a Crookes, Hittorf, or Lenard tube, having platinum
electrodes sealed in its ends, would, under the static discharge of
electricity through it, give peculiar manifestations of light. One of
the conducting terminals of such tubes was called, in electrical
parlance, the “anode,” from the Greek ανα (up) ὁδος (way), meaning the
way up or into the tube, and referring to the entering path of an
electric current, or its positive pole; while the other was called the
“cathode,” from κατα (down), ὁδος (way), meaning the way down or out,
and referring to the outgoing path of an electric current, or its
negative pole. When such glass tube, partially exhausted of air,
received through its anode and cathode terminals a discharge of static
electricity, a peculiar manifestation of light is seen between the anode
and cathode terminals. At the anode it appears as a peach blossom glow,
and at the cathode it appears as a bluish green light. If the exhaustion
of the air in the tube is carried very high, approaching a perfect
vacuum, or to about one millionth of the atmospheric pressure, the glow
light at the anode disappears, and that at the cathode increases until
it fills the entire tube with its characteristic light. This is called
the “cathode ray,” or “cathodic ray,” an illustration of which is given
in Fig. 215, where the cathode ray is seen in a Crookes tube emanating
from the negative pole N or cathode _a_, and casting a shadow of the
Maltese cross _b_ into the end of the tube, as seen at _d_. Many of the
characteristics of the cathode ray had been observed prior to Prof.
Roentgen’s discovery, which, briefly stated, grew out of the following
observation: He noticed that when a vacuum tube illumined by the cathode
ray was completely masked or covered up by an external shield of black
paper, so that no illumination of the tube was visible to the eye, there
still passed through it certain subtle rays of light, invisible to the
eye, but which would instantly illuminate a sheet of paper coated on one
side with barium platino-cyanide, even at a distance of two yards or
more, and that these invisible light rays were capable of passing
through many substances opaque to ordinary light. He also discovered
that these rays could be made to take a shadow photograph on a sensitive
plate without even exposing the plate in the usual way, the X-Rays
passing freely through the opaque ebonite or pasteboard screen of the
plate holder. It did not take the scientific world long to realize the
immense importance of this discovery, and to-day X-Ray apparatus
constitutes the greatest addition to the surgeon’s resources that has
ever been made in the form of mechanical appliances, since by its aid
any foreign body in the human frame of greater density than the flesh
may be at once definitely located and extracted, or any fracture of the
bone disclosed, as the case may be. In the illustration, Fig. 216, is
shown an X-Ray photograph of the hand of a gentleman whose thumb bone
has been destroyed by disease.
[Illustration: FIG. 216.--X-RAY PHOTO OF HAND, SHOWING DISEASED THUMB
BONE.]
Soon after the announcement of Prof. Roentgen’s discovery, apparatus was
devised for seeing with the naked eye the image formed by the shadow of
the X-Rays. Prof. Salvioni constructed such a device and described it
before the Rome Medical Society as early as February 8, 1896. He called
it the “cryptoscope.” It was quite a simple affair, and consisted of an
observation tube with a lens, having in front of it a screen of
fluorescing material, such as platino-cyanide of barium. When the object
to be examined, the hand, for instance, was held in front of the
fluorescing screen, and the X-Rays from the vacuum tube fell upon the
hand, located between the vacuum tube and the fluorescing screen, a
shadow of the bones was cast on the fluorescing screen by virtue of the
greater density of the bones, which shadow was clearly discernible to
the eye at the end of the observation tube. By this device one was able
to see his own bones through the flesh. A device, invented by Edison and
called the “fluoroscope,” was constructed on substantially the same
principle. This used a tapered observation tube like the old-fashioned
stereoscope box, which had at its outer wide end the fluorescing screen,
and its small end fashioned to fit the forehead and strapped thereto so
as to enclose both eyes. This device is shown in Fig. 217, in which an
X-Ray vacuum tube is housed in a wooden box, on which the hand of the
patient, or other part to be viewed, is laid, the X-Rays passing readily
through the top of the box and casting a shadow of the bones of the
hand, or foreign body, on the fluorescing screen of the observation
tube. Edison’s experiments also led him in constructing his fluorescing
screen, after testing a great number of substances, to select the
chemical known as calcium tungstate, instead of the barium
platino-cyanide, since the calcium tungstate appeared to give better
results in fluorescing. Many other chemicals can be used, however, for
making the fluorescing screen, such as the sulphides of calcium, barium
and strontium. A recently discovered and powerful fluorescing substance
is the double fluoride of ammonium and uranium, discovered by Dr.
Mecklebeke. Such fluorescing materials are spread in a thin layer on the
side of the screen next to the observer in the viewing apparatus.
[Illustration: FIG. 217.--EDISON’S SURGEON’S X-RAY APPARATUS.]
It is not to be understood that such viewing apparatus is necessary in
taking a surgical photograph. In such case only the X-Ray tube, means
for exciting it, the patient’s body, and the sensitive photographic
plate, are essential factors, the patient’s limb or body being
interposed between the light tube and photographic plate, so as to cause
the X-Rays emanating from the tube to cast the shadow of the patient’s
bones, the bullet in his body, or other foreign object, directly upon
the photographic plate, the sensitive and conscious plate obeying the
will of these subtle rays, and receiving the impress of their actinic
effect under conditions which it denies to ordinary light.
[Illustration: FIG. 218.--COMPLETE X-RAY APPARATUS IN USE.]
For exciting the vacuum tube any electrical machine capable of throwing
a series of sparks across a gap of about five inches is sufficient.
Various electrical machines may be used for this purpose, the Holtz, or
the Wimshurst glass plate machine, the Ruhmkorff, or induction coil, or
even the high frequency transformer. A good example of a complete X-Ray
apparatus is that in use at the Army Medical Museum at Washington, made
by Otis Clapp & Son, and shown in Fig. 218. The electrical generator is
of the Wimshurst type, and is shown in a large glass-enclosed cabinet on
the right. The glass disks within are rotated either by a small electric
motor shown on the floor, or by a hand crank above. The X-Ray tube, of
globular or bulb shape, is shown just above the patient’s hip, and its
opposite poles are connected by wires to the opposite electrodes of the
generator. When the current is switched on by the operator, the bulb is
illuminated with the cathode rays, and the X-Rays, proceeding therefrom
through the clothing and flesh of the patient, cast a shadow of the
patient’s hip joint upon the photographic plate placed on the cot
beneath the patient.
[Illustration: FIG. 219.--X-RAY FOCUS TUBE.]
In the effort to secure greater sharpness in the image cast by the
X-Rays, various forms of vacuum tubes have been devised. That shown in
Fig. 219 represents one of the most important improvements. K is the
cathode plate, formed of a concave disk of aluminum, which focuses the
rays at a point near the center of the bulb. At this point a plate of
platinum A, which metal allows practically none of the X-Rays to pass
through it, is mounted on the anode in such an angular position that it
gathers the focused rays and reflects them through the side of the tube.
They thus make a sharper shadow than when radiating from the more
extended surface of the glass.
[Illustration: FIG. 220.--LOCATING A FOREIGN BODY IN THE BRAIN.]
In Fig. 220 is shown an X-Ray tube, as applied for locating a foreign
body in the brain cavity, in which view the patient’s head is interposed
between the X-Ray tube and the fluorescing screen, or photographic
plate, as the case may be; while Fig. 221 shows the application of the
same devices to the body. In both these views the particular form of
X-Ray apparatus is known as the “Fluorometer,” made under the Dennis
Patent, No. 581,540, April 27, 1897, and it is devised with reference to
more accurately locating the foreign object by its shadow, for which
purpose adjustable bracket-sights, seen in Fig. 221 on opposite sides of
the body, are provided for bringing the X-Rays into proper alignment for
projecting the shadow of the foreign body in true indicative position on
the fluorescing screen, while a cross hatched grating behind the body,
graduated in aliquot spaces of an inch, furnishes a measured field, and
forms an easy and quick means of platting the position of said object.
In the position of parts in the two figures the horizontal line, on
which the foreign object lies, would be determined, but it would not
indicate how deep in the object was, _i. e._, whether it was in the
middle, or on one side. To determine this the fluorescing screen and
grating are placed under the patient, and the X-Ray tube above, and the
vertical line of the object is thus obtained. Both the vertical line and
horizontal line having been obtained, it will be obvious that the
foreign object will lie at the intersection of these two lines, which
establishes for the surgeon its definite location.
[Illustration: FIG. 221.--X-RAY APPARATUS APPLIED TO THE BODY.]
It has been observed by Prof. Elihu Thomson, and also by Dr. Kolle, that
the X-Rays are not absorbed and destroyed by the sensitive chemicals of
a single photographic plate, but so potent and penetrating is their
influence that the rays pass through and produce an image on a number of
plates, placed one behind the other, thus affording means for
multiplying the image at one exposure.
Among other uses of the X-Ray may be mentioned its capacity to detect
spurious from genuine gems, the diamond giving a distinct color from its
imitations, as do also most other precious stones.
A peculiar physiological effect of the X-Rays is their capacity to
produce a severe effect on the skin, somewhat resembling sunburn. Such
result, produced by long and continued exposure, has sometimes so
deranged the skin tissues as to make sores that resulted in the entire
loss of and renewal of the skin.
The discovery of the X-Ray by Prof. Roentgen may be fairly considered
one of the most wonderful scientific achievements of the century, and
his first memoir in 1895 is so full, clear and exact, as to have left
very little more to be said about it. It is to-day, as it was found by
him in 1895, the same mysterious, unseen, but positive force, a species
of electrical energy without a domicile, and needing no conductor, a
form of light passing through closed doors, invisible itself, and yet
lighting up certain substances with a halo of glory, and radically
changing and decomposing others. Rivaling the sun in actinic power, and
writing its autograph with an unseen hand, it is truly called the X-, or
unknown, ray.