394 WORK OF THE PHYSIOLOGICAL STATION AT PARIS. 



Many improvements have been made in tliis apparatns during recent 

 years. Quite recently two pupils of M. Frau^ois-Franck, MM. Halliou 

 and Comte, liave conceived a small instrument very simple and easy 

 of application. On introducing a. linger between two air cushions con- 

 nected with a grai)hic apparatus it is seen that this finger constantly 

 changes its volume, swells when its vessels dilate and diminishes as 

 they contract. Any pain felt by the subject under experiment, a simple 

 sensation of heat or cold, anj^ emotion, even if slight, is soon followed 

 by notable contraction of the vessels of the finger; that is to say, by a 

 lowering of the curve that is traced. (See fig. 2, PL XLVI.) 



We even find that in certain maladies an excitation not perceived by 

 the subject may give rise to a vascular contraction, which shows that 

 the seat of production of the vascular reflex is different from that of 

 conscious sensation. 



The possibility of transmitting to considerable distances by means of 

 air tubes the movements it is desired to record has mucli enlarged the 

 field of ajiplication of the graphic method. 



Thus we may in the case of a running man or a galloping horse note 

 the succession of footfalls or the cadence of the hoofs. In a flying bird 

 we may record the various phases of the action of its muscles, the trajec- 

 tory of a point of its wing, and tlie reactions thus effected upon the mass 

 of its body. But these experiments, although very carefully made, give 

 but a partial knowledge of the complicated acts of animal locomotion. 

 Another method, more prompt and more simple, records these move- 

 ments in a much more perfect manner. This is chrono-photography. 



I had the honor two years ago to make known to you the origin and 

 developments of this method. Since then I have improved it and 

 apidied it to the study of the most varied i)henomena. All these appli- 

 cations have been set forth in a little volume recently published.^ It 

 will be sufticient to say that besides the phenomena of physics and 

 mechanics, in which chrono-photography does most valuable service, 

 this method enables us to analyze the kind of locomotion used by most 

 species of animals, mammals, reptiles, birds, insects, fishes, etc. It may 

 even be used to register the movement of microscopic creatures. 



Chrono photography may therefore be considered as the most perfect 

 form of the graphic method. It is especially important when we have 

 to deal with very extensive or complicated movements, or, indeed? 

 when a movement has not sufiicient force to actuate the tracer of an 

 instrument. 



A record of the mechanical forces developed by animals may be 

 obtained by other apparatus, such as dynamographs, some of which 

 measure efforts of traction, others efibrts of pressure, and tliese, by the 

 way, must, like balances, be more or less strongly constructed according 

 to the amount of force to be applied. 



In order to give a complete idea of the physiological apparatus we 

 should also cite the instruments used to measure the eleetric currents 



' 1 Le Mouvemeiit, Paris, G. Masson, 1894. 



