The character of the illuminant also can be varied. Sunlight may be caught by the mirror of the microscope and projected through the instrument as well as the beam from an electric light, incandescent gas burner, or what not. With this effective and compact apparatus many marvellous microscopic experiments have been carried out at the Institute, such as the filming of the heart-beats of minute insects, and so forth. One very fascinating investigation was that carried out by Dr. J. Ries, of Switzerland, whereby he secured a cinematographic record of the different phases of the union of the sperm and the egg, as well as the separation of the membrane and segmentation of the sea urchin. The difficulties of such a delicate study were extreme, but the films obtained were of the utmost interest. They enabled the investigator to reconstruct upon the screen the complete phenomenon of fecundation. For this study the subject had to be photographed while immersed in a small vessel containing artificially prepared sea-water, which was renewed as required. The clock control enabled the camera mechanism to be so turned as to secure a regular series of exposures at the rate of seven per minute.
When Dr. Jean Comandon set himself to cinematograph the most minute microbes, which are so small that two million may be found in a cube measuring only one-twenty-fifth of an inch, he appreciated the limitations of the ordinary microscope, and the impossibility of obtaining images clearly and distinctly therewith. So he resorted to the ultra-microscope. With this instrument the light is not thrown directly through the slide containing the object, but is directed upon it by reflection from a light which stands at one side. Beneath the object to be examined is placed a glass prism, or condenser, set at right angles to the optical axis of the microscope, the result being that the light enters the slide through the edge. The objects under examination, instead of appearing as dark objects against a luminous ground as in the direct transmission of the light, appear luminous in themselves and stand out as bright spots against a dark background. By the aid of this instrument, particles which are beyond the scope of vision with the highest powered microscopes may be seen with ease.
Thus this French investigator was able to photograph even the most minute organisms. The well-known firm of Pathé Frères placed their laboratory and resources at his disposal, so that the work might be done under the most favourable conditions. Even then two years passed before a successful detailed film was obtained, and an apparatus made perfect for this class of work.
The complete apparatus is set upon a massive bench, so as to secure absolute rigidity, because vibrations are fatal to good results. Slight modifications are sometimes needed, but in most cases the same appliances are used, and in the same way. The light is furnished from a 30-ampère electric arc lamp. In front of this is arranged a series of lenses for concentrating and varying the rays, while all excess of luminosity is cut off from the microscope by means of a diaphragm. The microscope itself is set horizontally, with its longitudinal optical axis in line with that of the camera, and its eye-piece brought against the camera lens. The camera is one of the Pathé models with detachable dark-boxes.
The ray of light thrown from the electric lamp is concentrated and then falls upon the microscope condenser, which deflects it so that the objects under study become illuminated, no light entering the tube of the microscope. The camera may be turned by hand, or by a small electric motor, the latter giving an improved rotary motion with the least possible vibration.
The Micro-cinematograph used at the Marey Institute.
A. Special condenser. B. Electric arc light. C. Camera. D. Shutter between light and object. M. Microscope. O. Object under examination.
By permission of Pathé Frères.