APPARATUS FOR PHYSIOLOGICAL USE. 239 



our apparatus (Fig. 4) in such a way that we can obtain a 

 continuous record of the changes of diameter of the tube 

 which are taking place simultaneously at both ends and 

 in the middle, and compare the course of events at the near 

 end with what is happening during the same period at the 

 far end, we shall be able to see that the distension effect 

 gradually progresses from the former towards the latter. 

 For this purpose two little instruments, called tympana, 

 have been connected the one with the proximal end of 

 the supposed artery, the other with the distal end. Half 

 way between the two there is a third tympanum. Each 

 of these is connected in a manner which I shall explain 

 presently, with a second writing tympanum, by which its 

 motion is registered. "We thus get a triple tracing ; 

 one relating to the initial part of the artery, one to the 

 middle, and the other to the end part of it. [Here the 

 experiment was made.] It is not possible for you to see 

 the record which the three levers are tracing on the cylinder 

 while Mr. Page works the pump. I have therefore repre- 

 sented their characters in this diagram (Fig. 5). These black 

 lines on the diagram represent the three simultaneous tra- 

 cings made with the apparatus at different distances from the 

 initial point. The lower one is the graphic representation 

 of the distension wave, or rather waves, produced by a single 

 injection of liquid close to the pump; the second is the 

 tracing obtained when the tympanum is applied to the tube 

 about half-way between the starting-point and the end ; 

 the top line relates to the part of the tube close to its 

 extremity, where the water is continuously discharged by 

 an orifice considerably narrower than the tube itself. Let 

 me now draw your attention to the correlation of the 

 three tracings. In the lowest line you have the record of 

 a first distension, which is followed after a short interval 

 of time by another. In the second line the same thing, 

 with this difference that the interval between the primary 

 wave and its repetition is only half as long. The third line 

 exhibits the fact that at the end of the tube the wave is 

 not double but single. The meaning of these differences 

 is easy to understand. Just as when you make a series of 

 waves by throwing a stone into the centre of a pond, the 

 wave gradually progresses towards the side, and then 

 returns upon itself towards the centre ; so here in the case 



