ACTION OF DIGITALIS ON BLOOD PRESSURE. 103 



FiQ. 14. December 23. — Tracing at 5.30 p.m. Pulse, 68. Respiration, H2. 



Mj observations were now stopped, as I was going to the country; but from 

 tlie constancy of the characters of the pulse during the last four days, we may 

 suppose that it had now returned to its normal condition. 



EXPEEIMENTS ON THE INFLUENCE OF DIGITALIS 

 ON THE PEESSUEE OF BLOOD IN THE AETEEIES. 



In order to determine the influence exerted by digitalis, or digitaline, on the 

 arterial pressure, the carotid of a dog was exposed ; the nozzle of a hsema- 

 dynamometer inserted, and the height to which the column of mercury rose was 

 noted. After waiting a short time to see if the pressure was constant, digitaline 

 suspended in water, or infusion of digitalis, was injected into the jugular vein, 

 and the pressure again noted. 



The instruments which were commonly used consisted of a glass flask, partly 

 filled with mercury, into which two tubes dipped, and were held firm by being 

 cemented air- tight into a brass cap. The mouth of the flask is closed by an 

 india-rubber stopper, through which were passed a brass tube, provided with a 

 stop- cock, and having a funnel at its upper end. and a curved glass tube, by 

 means of which the instrument was connected to the artery. This brass nozzle 

 is small at the end, and grows rapidly wider, and is roughened at the small end 

 to prevent its being dragged out of the vessel by giving a better hold to the 

 ligatures securing it. By means of a piece of glass tubing, with a bulb upon it, 

 and india-rubber tubing, the nozzle was connected to the hsemadynamometer. 

 A clip was placed on the tubing, so as to restrain the flow of blood at pleasure. 

 The whole apparatus having been filled up to the end of the nozzle with a 

 solution of bi-carbonate of soda, to prevent coagulation of blood, poured in by 

 the funnel, the stopcock was turned, and the apparatus ready for use. A 

 graduated scale was applied to the tubes to show the height to which the 

 mercury rose. As the volume of mercury in the flask was so much greater than 

 that in the tube, no corrective was employed for the lowering in the flask as it 

 rose in the tube, as would have been necessary had a simple bent tube been used. 

 An apparatus of this kind, with a plain tube, gives trustworthy indications fo 

 long as the pressure is constant : but when it is variable, the indications become 

 fallacious from the mercury at each oscillation acquiring a rapidity which 

 carries it above and below the true maximum and minimum points. 



To obviate this, the compensating tube of Marey was used. This consists of 

 a tube, whose bore is reduced to a capillary size near the lower end. The 

 mercury can only pass through this very slowly, and the influenop exerted by 

 each oscillation on the height of tJie mercury in it being very small, the true 

 mean pressure of the blood is thus obtained. 



