The motion picture is an extremely valuable tool for the demonstration of facts. An old proverb reads: "One picture is worth more than many thousand words." The usefulness of the motion picture is especially obvious in medical science. Many records are made of surgical operations, of presentations of cases, etc. Today all the institutions of learning know the importance of the motion picture as a means of demonstration. By its domination of time, the motion picture is also a great help to research workers, especially where the human eye has its limits. We are chiefly concerned with the motion picture, especially the microscopic motion picture, as a means for investigation.The use of motion pictures for the analysis of movements of various subjects, especially men and animals, is as old as cinematography itself. I might call your attention to the experiments of Muybridge in America, and of Marey in France, about the year 1890. As a matter of fact we can safely say that the motion picture originated in the biological laboratory. Muybridge used a whole battery of still cameras, to be released by strings, which were placed in a row. In this way he took consecutive pictures of walking men and animals in order to study the various phases of their movements. Marey used for his experiments only one camera of the ordinary type, but placed in front of the plate a revolving shutter with slots in it, and made a number of exposures of the moving subject on the same plate. He studied, for example, the movements of a rabbit or a cat which had been dropped from a certain height. He also extended his researches to the study of flying birds by using a kind of photographic gun, and obtained consecutive pictures representing the progressive movements.
Until the later years of the nineteenth century the current view of the capillary circulation was that the capillaries were passive and that the rate of blood flow through them was determined by the state of the arteriole supplying them. Since then many researches have been carried out which show changes in the capillaries which the observers were unable to explain on the basis of arteriolar changes. The discovery by Rouget (1) of cells on the walls of the capillaries which he believed to be of a contractile nature lent strong support to the view that there is independent contractility of the capillaries. Of late years most observers agree that the capillaries both in man and in animals have the power of independent contractility. Whether they can do this normally without the application of a stimulus to them is disputed and there is also considerable doubt as to the mechanism which is involved in this action.The literature on the subject of capillary physiology has been so admirably reviewed by Krogh (2) that only some important points in the literature of more recent date will be referred to. There seems to be no doubt that the capillaries in both man and in animals can be made to contract by the application of suitable mechanical or chemical stimuli. It has also been definitely shown in animals that electrical stimulation of nerves can cause changes in the caliber of the capillary loops independent of the changes which take place in the arterioles. The work of Krogh (2) on the muscle capillaries has demonstrated that the number of capillaries in which blood is flowing is constantly changing and that the vascular supply is adjusted to the needs of the 351
Lombard (1) in 1911 showed that bv illuminating the skin the capillaries could be seen under the microscope. Since then many observations have been carried out on the changes which take place in these vessels in health and disease. The early observations which were made recorded the impressions of the author but had no quantitative basis. In recent years photographic records have been made by some investigators in order to study the changes which take pJace in human capillaries. This method is suitable for recording gross changes which last for a considerable length of time, such as comparing the form of the capillaries in different diseased conditions. Many changes which take place in the capillary circulation are however rapid and so fleeting that it seemed desirable, if they were to be placed on a quantitative basis, to obtain records at a more rapid rate than one could do by ordinary photography. It seemed possible that cinematographic records would enable one to follow these changes and subsequently analyse them in detail by measurement.The possibility of studying alterations in the capillaries by means of cinematography first suggested itself to Krogh and Rehberg (2). They developed a method of taking photographs of the circulation in the capillaries in the tissues of Rana temporaria. It is naturally simpler to obtain records from the tissues of frogs than from human tissues since for this purpose a technique resembling that used in histological photomicrography suffices. In the human case, however, transmitted light cannot be used, so Lombard's method of illumination from above has been universally adopted. This method is difficult because by it contrast and intensity of light are much reduced com-343
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