Professor Chemistry and Toxicology, N. Y. Hom. Med. College and Hospital.

U

NTIL quite recently, Geissler tubes, Hittorf and Crookes'

tubes were nothing more or less than a scientific curiosity. Beautiful enough indeed are the appearances which they exhibit. Geissler tubes differ from the other in as far as the air is not as thoroughly evacuated from them. In the Hittorf or Crookes' tube, the attenuation is supposed to be carried on to one millionth. All of these tubes are supplied with electrodes, so that a current can be sent through the inner space. This current has to travel on something less than ordinary air, since the poles are fixed at the inner terminals of the tubes. In common air or in undiluted gases, the traversing of the current results in appearances of incandescence. In the attenuation reached in the Geissler tube, beautiful phenomena of luminosity appear when the spark of an induction coil is applied. "The sparks become less sharply defined and widen out to occupy the whole tube, becoming pale in tint and nebulous in form. The cathode exhibits a beautiful bluish or violet glow, separated from the conductor by a narrow black space, while at the anode a single small star of light is all that remains. At a certain degree of exhaustion the light breaks up into a set of striae or patches of light of cup-like form, which vibrate to and fro between darker spaces." -(Silvanus P. Thompson).

In high vacua, the dark space separating the negative glow from the negative pole increases in width. If exhaustion be carried

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to such a degree that the dark space fills the entire tube or bulb, the glass walls become beautifully phosphorescent.-(Thompson).

Hertz found that the cathode "rays" which will not pass through glass, mica or any transparent substance, will pass through metal foil.

Lenard, using a vacuum tube with a window of aluminum foil at one end, succeeded in passing the cathode rays out into the air (in which they cannot be produced at all) and found that they then retained their remarkable property of exciting phosphorescence.

Roentgen allowed these rays to impinge upon a sensitive photographic plate, enclosed in a plate holder and obtained shadow pictures of certain objects placed on top of the plate holder. Roentgen does not know what, exactly, is the kind of "radiance" which produces this effect, but he does claim, that it is something different from the cathode ray, since that radiance which is photographically active can not be refracted nor polarized. The radiance in question,

which at present excites the curiosity of the world, passes through some substances and not through others. It does not affect the human retina so as to produce that sensation which we call light. It exerts a chemical action upon silver bromid, decomposing it where it strikes. Thick layers of certain metals do not allow it to pass through. Aluminum does. A block of oak wood of 41⁄2" diam. is no hindrance to them. Roentgen was led to the experiment with sensitive plates by the observation that the phosphorescence of outside objects (screens covered with calcium-platinic-cyanid) obtained, even if the Hittorf tube was contained in a dark box.

As far as the application of this new-born babe for the purpose of medical diagnosis is concerned, very little can be said as yet.

The bone substance, bullets, needles or pins will not allow the radiance to pass through, consequently the photographic plates will

show their presence in the form of shadows. These shadows are very often distorted or enlarged, according to the angle under which the rays strike the object. Unfortunately, however, the soft tissues

throw no shadow, or very little of it.

If at a future time it should become a possibility to construct tubes so as to enable their introduction into cavities of the body, the stomach, intestines, pelvis, etc., and if shadow pictures of softer tissues could be produced differing in shade from less soft tissue, then this discovery will, we trust, be of general application. A slight advance will have been made, when the physician, through a phosphorescent screen and a dark box, shall LOOK at the shadow picture produced upon this screen, thus avoiding the loss of time. caused by the process of photographing.

In the meantime, it appeals to the philosophic mind, urging it to speculate upon what is the nature of this radiance and, let us hope, that on the path of these speculations, new appearances will spring up, new facts will be found, widening the narrow bounds within which human conception is doomed to move.

H

REVIEW OF THE MINERALS.*

BY GEORGE ROYAL, M.D.

Professor of Materia Medica, University of Iowa.

Des Moines. Iowa.

AVING to-day finished the study of the minerals and their compounds used by Homœopathists as remedies, I feel that we can now spend the hour to advantage, in a hurried review of them taken as a group.

I have placed upon the blackboard, what for want of a better name we will call a chart, in order that the sense of sight may assist the sense of hearing to fix in our minds some of the facts considered during the winter.

The first thing we will notice is that many of these minerals are the inorganic constituents necessary to the formation, development and preservation of the human body.

To the Junior class all prepared for your final examination the histological and physiological action of the list of elements I have placed under the first heading is familiar. The Senior class will recognize the compounds which I have grouped in the second class as combinations of those found in the first which, together with Silicea, constitute the twelve tissue remedies of Schüssler. The

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