By WILLIAM GILMAN THOMPSON, M.D., New York.
The apparatus was devised by Mr. R.D. Gray (the inventor of the ingenious "vest camera" and other photographic improvements) and by myself. I described what was required and suggested various modifications and improvements, but the mechanical details were worked out exclusively by him. To test the rapidity of the camera, we photographed a "horse-timer" clock, with a dial marking quarter seconds, and succeeded in taking five distinct photographs in half a second with one lens, which has never before been accomplished excepting by Professor Marey,1 at the College de France, who has taken successive views of flying birds, falling balls, etc., with one lens at a very rapid rate. His camera was unknown to me until after mine was constructed, so that as a success in photography alone the work is interesting.
The camera consists of a circular brass box, 5½ inches in diameter and 1¼ inches deep, containing a circular vulcanite shutter with two apertures, behind which is placed a circular dry plate. Both plate and shutter are revolved in opposite directions to each other by a simple arrangement of four cogged wheels moved by a single crank. The box is perforated at one side by a circular opening, 1¾ inches in diameter, from the margin of which projects at a right angle a long brass tube (Fig. 1), which carries the lens. In Fig. 2 the lid of the box has been removed, and the bottom of the box, with the wheels, springs, and partially closed shutter, is presented. The lid is double - that is, it is a flat box in itself. It contains nothing but the dry plate, supported at its center upon a small brass disk, against which disk it is firmly pressed by a pivot attached to a spring fastened in the lid. The aperture in one side of this double lid, which corresponds with that seen in the floor of the box, may be closed by a slide, so that the lid containing the plate can be removed like an ordinary plate holder and carried to a dark room, where it is opened and the plate is changed.
When the lid is replaced this slide is removed, and as the shutter is made to revolve, the light falls upon whatever portion of the dry plate happens to be opposite the opening.
By reference to Fig. 2, it will be seen that when the large wheel which projects outside of the box is revolved by a crank, it turns the small ratchet wheel, which bears an eccentric pawl. (The crank has been removed in Fig. 2; it is seen in Fig. 1.) The central wheel has only six cogs. The pawl is pressed into one of these cogs by a spring. It pushes the central wheel around one-sixth of its circumference, when it returns to be pressed into the next cog. While the pawl returns, it necessarily leaves the central wheel at rest, and whatever momentum this wheel carries is checked by a simple stop pressed by a spring upon the opposite side. The central wheel carries a square axle, which projects through a small hole in the center of the double lid and fits into the brass disk before alluded to, causing the disk to revolve with the axle. The disk is covered by rubber cloth; and as the dry plate is pressed firmly against the rubber surface by the spring in the lid, the plate adheres to the rubber and revolves with the disk. Thus every complete revolution of the central wheel in the floor of the box carries with it the dry plate, stops it, and moves it on again six times.
The velocity of revolution of the plate is only limited by the rapidity with which one can turn the crank.
The shutter is revolved in the opposite direction by a wheel whose cogs are seen fitting into those of the little wheel carrying the eccentric pawl.
FIG. 1. - THE CAMERA MOUNTED.
The two apertures in the shutter are so placed that at the instant of exposure of the plate it is momentarily at rest, while the plate when moving is covered by the shutters. This arrangement prevents vibration of the plate and blurring of the image. The camera is mounted by two lateral axles with screw clamps upon two iron stands, such as are in common use in chemical laboratories. A brass rod attached to the tube steadies it, and allows it to be screwed fast at any angle corresponding to the angle at which the heart is placed. It is thus easy to put a manometer tube in the femoral artery of an animal, bend it up alongside of the exposed heart, and simultaneously photograph the cardiac contraction and the degree of rise of the fluid in the manometer(!). The tube is arranged like the draw tube of a microscope. It is made long, so as to admit of taking small hearts at life-size. The stand carries a support for the frog or other animal to be experimented upon, and a bottle of physiological salt solution kept warm by a spirit lamp beneath.
FIG. 2. - INTERIOR OF THE CAMERA.
The whole apparatus is readily packed in a small space. I have already taken a number of photographs of various hearts and intestines with it, and the contraction of the heart of the frog produced by Strophanthus hispidus, the new cardiac stimulant, is seen in Fig. 3, taken by this new instrument. The apparatus has the great advantage that six photographs of a single cardiac pulsation, or of any muscular contraction, may be easily taken in less than one second, or, by simply turning the crank slower, they may be taken at any desired rate to keep pace with the rhythm of the heart. The second hand of a watch may be placed in the field of view and simultaneously photographed with the heart, so that there can be no question about the series of photographs all belonging to one pulsation.
FIG. 3. - PHOTOGRAPHS OF THE HEART IN MOTION.
1, Normal diastole; 2, auricular systole; 3, ventricular systole. 1, 2, 3 were taken in a half second; 4, 5, 6, same as 1, 2, 3, after injection of toxic dose of Strophanthus hispidus. 4, 5, 6 were taken in a half second. The pulse rate was 74.
I have already called attention2 to the ease with which these photographs are enlarged for lecture room demonstration, either on paper or in a stereopticon, and the ease with which they may be reproduced in print to illustrate the action of drugs.
La Methode Graphique (Supplement), Paris, 1885.
Medical Record, loc. cit.; Recent Advances in Methods of Studying the Heart, Medical Press, Buffalo, March 1, 1886, p. 234; Instantaneous Photographs of the Heart, Johns Hopkins University Circulars, March, 1886, p. 60.