168 EXPERIMENTAL PHYSIOLOGY 



CHAPTER XVII 



DEMONSTRATION OF BLOOD PRESSURE AND ITS NERVOUS 

 REGULATION 



For this experiment the following apparatus is necessary (fig. 132). The 

 writing surface consists of an endless roll of blackened paper stretched between 

 two drums, one of which can be rotated at a slow rate by a tangent screw in 

 the ordinary manner. The recording levers consist of a tambour, t 2 , to record 

 the respiratory movements, a mercury manometer, m, with float, w, and two 

 chronographs, cc. All these writing points are arranged of such a length and 

 in such position that all lie in the same vertical line on the recording surface. 

 Of the two chronographs the lower one is connected to a clock, cl, ticking 

 seconds and a battery, b-. Attached to the escapement of the clock is a wire 

 which each second dips into a cup of mercury (seen vertically below cl in the 

 figure), thus closing a circuit and actuating the chronograph. The upper 

 chronograph is arranged to record the zero pressure, and is also utilised to 

 mark the instant at which any stimulation is made. For this purpose it is 

 connected in series with a battery b 1 , the two pillars of a coil a and a key k. 

 On closing k the Neef s hammer vibrates, and with each rise and fall of the 

 hammer the chronograph lever rises and falls. To the terminals of the 

 secondary coil a pair of shielded electrodes, e, is connected. 



To record the respiratory movements for this experiment a receiving 

 tambour, t\ is fitted on a horizontal rod with the rubber membrane facing 

 downwards. To the centre of the membrane a cork is cemented and the 

 tambour is then held over the rabbit in such a way that the cork rests on the 

 abdomen at a part that moves freely with each respiration. This tambour 

 is connected by rubber tubing, into which a -piece is inserted, with the 

 recording tambour t 2 . With each inspiration the abdomen rises, forces air 

 out of the tambour t 1 into the tambour t 2 , the lever of which therefore rises. 



The mercury manometer consists of two vertically placed glass tubes of 

 equal bore, about half-filled with mercury. In one of these a float, w, rests 

 on the upper surface of the mercury. The other is connected by a piece of 

 thick-walled pressure tubing to a pressure bottle, pb, which is filled with a 

 half-saturated solution of sodium sulphate. A spring clip, l, controls the 

 connection of the pressure bottle with the manometer. This second tube of 

 the manometer is connected by a lateral piece with a metal tube on which is 

 a tap, s, and this, by rubber tubing of narrow bore and thick walls, can be 

 connected to the cannula in the artery. 



The apparatus being prepared, a rabbit is tied down to a holder and put 

 under ether. Its head is then fixed by a Czerrnak's rabbit-holder. A 

 median incision is made through the skin of the neck for about four inches, 

 so as to expose the larynx at the upper end of the incision. The platysma is 

 cut through in the mid-line. The sterno-mastoid is separated from the sterno- 



