EVENING DISCOURSES. 821 



figure the principle of a diving-bell or submarine-boat. Marey points out that 

 Borelli gave the first correct explanation of the flight of a bird. The wings act 

 on the air, as he said, like a wedge — after the manner of an inclined plane — in 

 order to produce a reaction against the resistance of the air whereby the body of 

 the bird is driven forward. Marey himself admits the correctness of Borelli's 

 theory, while modestly only claiming for himself the subordinate merit of having 

 furnished the demonstration of a truth already suspected. 



The Graphic and Photographic Methods. 



The introduction of exact physical and chemical methods completely revolu- 

 tionised the subject of physiology, especially from the period of Johannes Muller 

 onwards. On the physical side no method contributed more to this advance than 

 the 'Graphic Method.' It is a very remarkable fact that though man for cen- 

 turies—indeed, for thousands of years before the Israelites crossed the Eed Sea, 

 about 1500 B.C. — had been writing or recording his thoughts in various graphic 

 characters, by the skilled movements of his own right hand, on stationary surfaces, 

 it was only about six decades ago that the movements of other parts of his 

 mechanism were recorded on a moving surface driven by clockwork. A more 

 exact analysis and interpretation of animal movements was not possible until the 

 graphic method had been applied to the study of movements which are either too 

 rapid or of too short duration to be followed by the unaided eye. About 1800 

 Thomas Young recorded time by means of a vibrating metallic rod on the surface 

 of a cylinder. James Watt inscribed the movements of the indicator of his steam- 

 engine on a cylinder, moved by the engine itself. In physiology the impulse 

 towards the application of the graphic method came through Carl Ludwig in 1847, 

 when he invented an instrument which he called a ' Kymographion,' or Wave- 

 writer. Thus for the first time was recorded the beat of the heart as expressed in 

 the variations of pressure within the arteries. I shall show you to-night a lantern- 

 slide copied from the original tracing taken by Ludwig on December 12, 1846. 

 I owe this to my friend Professor A. Mosso, of Turin, to whom Ludwig presented 

 a portion of the original tracing. 



The graphic method was rapidly extended to the study of all kinds of 

 physiological and other phenomena. New apparatus in the form of ' myographs ' 

 and other recording instruments were invented. Time was accurately recorded by 

 vibrating tuning-forks and by chronographs. Problems deemed insoluble a few 

 years before, thanks to the labours and investigations of Helmholtz, du Bois 

 Reymond, and above all to Professor Marey, of Paris, were brought within the 

 range of the experimental method. More, however, was still required. Photo- 

 graphy soon lent its aid, and to-night I shall show some remarkable results of the 

 application of cinematography to the study of physiological movements as ex- 

 hibited by the microscopic forms of life so numerous in water, as well as the 

 movements of parasites that live in the blood, and are the cause of some of the 

 most fatal diseases to which man and animals alike are subject. This I am able 

 to do through the kindness of Messrs. Pathe Freres and Dr. Comandon. My best 

 thanks also are due to the Gaumont Co., Ltd., for recording for me a special 

 series of films expressly taken to illustrate this lecture, but which, I hope, may 

 prove useful to other physiologists. I believe there is a great future for the 

 application of the cinematograph to physiological problems, both as a means of 

 investigation and in teaching. 



Notes on the Illustrations. 

 The first type of animal movement selected was that of Amoeba; lantern 

 slides were shown to indicate its changes of form, mode of feeding, movements 

 and reactions to stimuli such as have been described by Jennings. Many attempts 

 have been made to explain Amoeboid movements by artificial imitations of proto- 

 plasmic activities. The imitations are based on the assumption that these 

 phenomena in Amoeba and other protoplasmic masses are due to local changes of 

 surface tension in a fluid mass— a view associated with the names of Quincke 

 Butschli, Rhumbler, and others. Gad, in 1878, placed a drop of rancid oil on a 

 dilute solution of carbonate of soda. The fatty acid acts on the oil, a soap is 

 formed ; this lowers the surface tension at various points of the drop 'of oil and 

 as a result the drop changes its form and sends out projections having an external 



