PRACTICAL CONDUCT OF EXERCISE VIII 145 



upper part of the block. To the body of the block between the two side tubulures is 

 screwed a rectangidar brass piece which carries in the limbs of a yoke two small screw 

 pins on which the writing-lever is pivoted. The stem of the writing-lever passes above the 

 centre of the rubber membrane which forms the roof of the shallow cup-chamber. The lever 

 where it crosses the membrane rests on a little aluminium saddle which is secotined 

 centrally to the top of the membrane. The writing-lever is a small straw tipped with 

 a little paper point, as light as possible. The bearing of the lever is adjustable in relation to 

 the membrane by tilting the brass yoke-piece which carries it. 



A rubber disk suitable for the manometer can be cut from a Martin elastic surgical 

 bandage, gauges 21, 22, or 23 ; or from a piece of bicycle-wheel tyre's inner tubing. ^ Dress- 

 improver ' rubber is too thin for this sized capsule. For cutting the disk, which must fit the 

 capsule shelf accurately, a cork-borer of appropriate diameter answers, but a steel pmich 

 is better, the rubber for cutting lying on the cross-grain of a piece of hard wood. For 

 connecting arterial cannula with manometer, rubber-pressure tubing of 2 mm. bore is 

 better than the 2*5 mm. bore used for the other kymographic exercises. The connecting- 

 tube should be as short as practicable, e. g. 20 cm. The subclavian artery, where used for this 

 experiment, will take a wider-nozzled cannula than the carotid ; if well sloped off the nozzle - 

 point can have an external diam. 2-3 mm. If the left subclavian be used low down there 

 is no need for separate ligation of the left internal mammary. 



A difficulty which may meet the student is that in pushing the stylet down against the 

 valve to rupture a cusp the stylet may drag the innominate and tear that vessel where it was 

 cut partially through for admission of the stylet. There is then less to hinder the valve 

 retiring before the stylet without breaking, and to break it becomes difficult. To avoid the 

 innominate's tearing and yielding it is well to hold, when inserting the stylet and when 

 pushing the stylet against the valve, the innominate itself, not by the ligature tied round its 

 distal end, but by grasping with the dagger-tipped forceps one edge of the cut opening in the 

 artery. 



During the manipulation for breaking the valve the lie of the cannula connecting left 

 subclavian artery with the manometer may be shifted, so that the line of connexion of that 

 artery with manometer becomes partially kinked. Such a shift at once impairs the height 

 of the oscillations of the pulse record which it is a main object of the exercise to study in 

 comparison with those obtained before the valve is broken. 



EXERCISE IX 



Obs. 39. The method of Anderson. Jnl. of Physiol, vol. xxxi, Proc. Physiol. Soc. p. xxi, 

 1904, for exposing the accelerantes gives an excellent exercise. As here adopted the opera- 

 tion wound is large, but the result unfailingly successful. The student can restrict his 

 opening incisions somewhat at a second performance of the exercise. Unipolar faradization 

 has some advantages for the stimulation of the exposed nerves. 



Obs. 41. In providing the decapitate preparation for this exercise it is well for the 

 tracheal cannula inserted to be one with external branches as short as practicable and to be 

 put into the trachea low down near the sternum, care being taken not to include the recurvent 

 laryngeal nerves in the ligature securing the cannula. In severing the neck the decapitating 

 knife may with advantage be carried forward ventrally somewhat farther than usual, thus 

 retaining as amply as possible for the student the parts about larynx and epiglottis. 



8131 XJ 



