BLOOD PKESSUKE AND PULSE PATE. 279 



tions in the puls3-rate and blood-pressure which we meet with 

 in disease, as well as those prochiced by drugs, are due to some 

 one or other of the causes mentioned in the previous table ; and 

 whenever you meet with a quick, slow, weak, or irregular pulse, 

 you must try to find out to which of these causes it is due,, in order 

 that you may be able to apply scientifically the proper remedy. 



Experimental Examination of Blood Frcssure: Forms of 

 Manometer. — As the life and health of the body and of the 

 organs comprising it depend on the supply of blood to them — 

 and this, as we have already seen, is closely associated with the 

 arterial pressure — the observation of the effects of drugs on it 

 naturally forms one of the most important parts of an investi- 

 gation into their action. The first to measure the blood-pressure 

 was Hales, who simply connected a glass-tube with an artery, 

 and noted the height to which the blood rose in it. Poiseuille 

 improved upon this method by substituting a bent tube, par- 

 tially filled with mercury, for the straight tube, and estimating 

 the pressure from the ditference in the level of the mercury in 

 the two limbs. A solution of carbonate or bicarbonate of soda 

 was introduced into the tube between the mercury and the 

 blood in order to prevent its coagulation. The bent tube, 

 partly filled with mercury, is called a haemadynamometer, or, 

 more generally, a manometer. The height of the mercury is 

 read ofi" from a scale fixed behind the tube. Usually both limbs 

 of ihe tube are of equal diameter, and the blood-pressure is 

 then ascertained by doubling the height of the mercury above 

 zero in one limb and subtracting a fraction, which varies with 

 the specific gravity of the solution of soda used. The height 

 must be doubled, because the mercury descends as much below 

 zero in the one limb as it rises above it in the other ; and a 

 fraction of the whole is subtracted for the additional weight of 

 the column of soda solution, which enters one limb as the 

 mercury rises in the other. 



A very simple manometer, which will show the mean blood- 

 pressure as well as the maximum and minnimm between which 

 it oscillates, may be made by passing two straight glass-tubes 

 about 16 inches long through the cork or india-rubber stopper 

 of a small wide-mouthed bottle, and fixing behind them a 



