48 W. G. SMITH : could be registered in graphic form. The instrument first employed was a sphygmograph used for transmitting pulse movements to a distance, the finger being rested on the button which is applied to the artery : connexion was made by rubber tubing with a Marey tambour the lever of which made a tracing on the smoked surface of a rotating drum. In some of the later experiments the sphymograph was replaced by a piece of medium-sized rubber tubing lying on the table. The variations in the pressure of the finger are not registered so delicately when the tubing is used, but there is this de- cided advantage, that the antagonistic reactions, which are sometimes energetic, cannot make the extensive and trouble- some tracing which is possible when the sphygmograph is employed. Time determinations were made by means of a time marker connected with an electric tuning fork giving 100 vibrations per second. The method first employed was that of allowing the time marker to begin marking hundredths simultaneously with the presentation of the stimulus. This FIG. 1. The curve is to be read from left to right ; a, point of stimulation ; 6, rise of antagonistic curve ; c, apex of this curve. method however, though very convenient, requires certain corrections to be applied to the figures obtained, and in the later experiments (those summarised in Table I.) the method was adopted of having three simultaneous tracings in each reaction. One of these indicated the nature of the reagent's pressure or movement, one gave a continuous time tracing, while a third indicated the moment when the stimulus was given. A reproduction of a typical antagonistic reaction with accompanying tracings of time and stimulus is given below. It may be remarked that while in the ordinary form of reaction the lifting of the finger causes a fall in the curve which indicates the reagent's movement, in the antagonistic form the downward pressure of the finger causes a preliminary rise in the curve. In the later experiments the reaction time was determined both graphically and by means of the Hipp chronoscope. The arrangement of the electric circuit employed was that in which the current actuates the magnets of the chronoscope
