WORK OF THE PHYSIOLOGICAL STATION AT TAKIS. 399 



At any rate these experimeuts liave clearly sbowu that muscular 

 forces behave in their final result like other mechanical forces. 

 New problems are uow placed before us; let us examine them. 



III. 



The analysis of the movements of man and animals may be made 

 from different points of view. It is, indeed, not sufficient to determine 

 the external characters of the movement; the important matter is to 

 ascertain the mechanism by which that movement is effected and to 

 distinguish the part played by the different portions of the locomotor 

 apparatus, muscles, articular surfaces, and osseous radii. 



To adapt it for these different researches chronophotography inay be 

 employed in different ways,' sometimes using a movable plate and some- 

 times a fixed plate. 



When it is wished to record the movements as a whole, it is necessary 

 to use cbrono-photography on a movable plate, for it gives a series of 

 entire images of the subject in action. Thus PI. XLVII, which shows 

 seven different attitudes of a person taking a step in walking, gives the 

 necessary information concerning the velocity and the extent of the 

 displacements of the body and the limbs as well as the state of con- 

 traction or relaxation of certain muscles shown in relief under the skin. 

 But in order to be well understood tliese independent images should be 

 placed in their relative positions, and this is done by means of a series 

 of successive tracings, examples of which will shortly be given. 



This laborious and delicate operation makes the analysis of move- 

 ment a long process: this may, however, be shortened in certain cases. 

 It was just because I wished to get, at a single exposure, a photo- 

 graphic outline of a movement that I conceived the idea of chrono- 

 photography upon a fixed plate. AVitli this method it is true the 

 images of a moving man or an animal are reduced to a few brilliant 

 points and lines, but this is generally sufficient to mark the action of 

 the limbs in the different gaits. 



It is not only in locomotion properly so called that movements occur 

 that are of scientific interest; mastication, respiration, speecli, expres- 

 sion of the countenance, partial movements of the limbs, hands, or feet 

 are of no less interest. 



Suppose, for example, that it is desired to ascertain the movements 

 of the lower jaw by chrono-photography on a fixed plate. 



The teeth of the lower jaw, first well wiped, are idaced in one of 

 those metallic molds fall of wax, which dentists use for taking impres- 

 sions. Upon this solid base there is fixed a bright metallic rod (fig. 1, 

 PI. XL VIII), whose angular curvature exactly follows that of the lower 

 jaw. This rod, placed outside of the jaw, shows clearly upon a small 

 piece of velvet that forms for it a dark background (fig. 2, PI. XLVfll). 



1 See Le Mouvemeut, Chapters IV and VII. 



