282 EXPEELMEXTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



attached to c, and may be connected with the tube B in the artery by a piece of 

 india-rubber tubing. It ia bored in a T-shape, and is perforated in the centre 

 by an additional perpendicular hole, into which is put a hollow plug e. f is a. 

 flask containing saturated solution of bicarbonate of soda, and connected by 

 india-rubber tubing with e. When the clip on the india-rubber tube just above 

 € is removed, and the stopcock turned longitudinally, soda solution will flow into 

 c as well as out of d. By tui^ning it transversely, the opening towards c may be 

 closed, and soda will then only run out thi'ough d. This is done when we wish 

 to wash out the cannula with soda without altering the level of the mercury in a. 

 ^ is a glass pen attached to the top of a glass rod or swimmer, which rests on the 

 surface of the mercury in a. A is a thi'ead of unspun silk, with a small weight 

 attached to it. It rests against the pen ff, and keeps it constantly applied to the 

 paper without impeding its movements, i is an iron wire, from which the 

 thread h is suspended. J is the wooden frame bearing the clockwork and 

 revolving cylinder, k are three screws to level the frame. I is the clockwork. 

 m is an iipright, and n a horizontal bar, which support a pivot o. jt? is a metal 

 cylinder, which carries the paper. 5- is a small metal bar for holding the paper 

 on the cylinder. It is hinged to the lower edge of the cylinder, and cauglit by a 

 spring at its upper edge. It lies in a hollow in the cylinder, so that its outer 

 surface does rot project above it. When a new paper is to be put on, the spring 

 catch at the upper end of q is raised, q pulled out, the old paper removed, and 

 the edges of the new one pla ed under q. It is then pushed down, its upper 

 end is caught by the spring, and the paper is securely held, r is a catch for 

 stopping the movement of the clockwork, s and s' are two weights to drive the 

 clockwork. ^ is a rack for winding up the weight /. w is a pendulum, with a 

 movable bob, to regulate the motion of the clockwork and cylinder. By moving 

 the bob up or down, the motion may be made quicker or slower, -y is a pencil 

 stuck through a piece of cork and fastened to the upright m, so as to draw a 

 Jine on the paper at the same level as ff, when there is no pressure on the 

 mercury in the tube. The blood-pressure is estimated by the lieight of the 

 curve traced by ff above the zero line thus drawn. 3/ is one of Marey's tympana, 

 which is supported on a movable rod z, and may be -^ised for registering either 

 the respiration or the form of the pulse-wave. It consists of a sliallovv cup of 

 metal, over whose top a piece of india-rubber is tightly stretched. A metal 

 tube passes into the interior of the cup, and a light kver lies over the upper 

 surface of the india-rubber and is firmly connected with it. When air is blown 

 into the interior of the cup, the india-rubber bulges and raises the lever; when 

 air is sucked out, it becomes depressed and draws the lever down. When used 

 to register the respirations, it is simply connected with a tube in the trachea of 

 the animal, or with a mask fitted before its nose. As the piece of india-rubber 

 stretched over y is thin, it would be blow^n out, and perliaps burst, by the 

 prc^ssure, if we were to connect it directly with the artery. One of Marey's 

 sphygmoscopes is, therefore, introduced between them when we wish to measure 

 the blood-pressure. The sphygmoscope consists of a little bag of strong india- 

 rubber, enclosed in a piece of glass tubing, connected with the tympanum. The 

 bag is filled with soda solution and connected with the artery. Each time that 

 the pressure rises in the artery, the bag becomes distended and forces some of 

 the air out of the glass tube into the tympanum, and raises the lever; and when 

 the pressure diminishes, the bag collapses again and the lever falls, a? is a 

 modification of this, designed by my friend Dr. Burdon Sanderson. Instead of 



