280 EXPEKIMENTAL INVESTIGATIOX OF THE ACTIOX OF lAIEDICIXna 



graduated cardboard scale. The lower end of one tube must 

 be nearly closed in the blow-pipe llame, and both pushed down 

 till they almost touch the bottom of the bottle. A third bent 

 tube is inserted into the stopper, reaching only to its under 

 surface, and a piece of india-rubber tubing is attached to its- 

 upper end for the purpose of connecting it with the artery. 

 Some mercury is then poured into the bottle, so as to stand a 

 little above the ends of the tubes, and both it and the india- 

 rubber tube are filled with a saturated solution of bicarbonate 

 of soda and connected with the artery. The mercury rises and 

 falls in the open tube with every pulsation ; but in the one 

 with the constricted end the resistance to its movement is so 

 great that it can only rise and fall slowly, so that, before its 

 upward oscillation has had time to .-how itself, its descent has 

 begun, and vice versd. TJie upward and downward oscillations 

 thus balancing each other, the mean pressure only is shown 

 (vide pp. 103 and 104). 



The oscillations in the unconstricted tube are so rapid that it 

 is impossible for the eye to follow tliem exactly; and this dild- 

 culty led Ludwig to conceive the idea of making them register 

 themselves by means of a slender rod swimming on the surface 

 of the mercury, and bearing at its upper end a pen which 

 moved up and down on a piece of paper fixed on a revolving 

 cylinder. The vertical lieight of the tracing thus produced 

 showed the blood-pressure, while tlie horizontal distance from 

 one point to another on it indicated the time between them. 



This instrument is called a kymographion ; and, in dtnising 

 it, Ludwig introduced for the first time into physiology that 

 method of self-registration which is now genei-ally applied te 

 all kinds of vital phenomena, and has already done much 

 to render our knowledge exact. That form of it which is used 

 by Traube, and made by Sauerwald, of Berlin, is shown in 

 rig. loo. It consists of a metal cylinder (2)) supported on a 

 wooden frame (j), and caused to revolve at a steady rate by 

 clockwork and pendulum (I and u). The manometer is fixed to 

 the wooden frame and connected with the artery by tubing of 

 lead and india-rubber. On the mercury in one limb floats a rod 

 or swimmer of glass, to whose upper end is attached a glass 



