34 



EXERCISE V 



yield, slight inertia, and perfect elasticity, 

 applied to the artery directly, or by very 

 short and restricted fluid connexions. Your 

 graphic records in the exercise, therefore, 

 although perfectly reliable for the slower 

 changes of pressure, do not show adequately 

 either the extent or the details of the pulse- 

 curve ; you can see this by comparing them 

 with pulse-records taken with the sphygmo- 

 graph, or with records you will obtain (exerc. 

 VIII) when using the rubber membrane- 

 recorder. 



The mean arterial pressure as you find it 

 in this exercise is considerably lower than 

 that of the normal cat, since the bulbar 

 vasomotor centre has been removed by the 

 decapitation, and the arterial wall throughout 

 the systematic system is therefore relaxed. 

 The distribution of blood owing to this 

 abnormal dilatation of the arterioles departs, 

 therefore, from its normal relative pro- 

 portioning in arteries, capillaries, and veins 

 respectively; the arteries are underfilled, 

 the veins are somewhat overfilled, which 

 latter circumstance facilitates your intra- 

 venous injection with the needle-syringe. 



Ohs. 20, 21. Unipolar faradization is 

 particularly suitable for stimulating nervous 



surfaces where the direction of the fibres to 

 be excited lies mainly at right angles to the 

 plane of the surface. It is therefore fitted 

 for experiments on point to point stimulation 

 of cut planes of the central nervous system 

 or the natural surfaces of the bulb or cortex 

 cerebri. It is also often useful for stimu- 

 lating peripheral nerves which are difiicult 

 of access, by reason of the cut stump being 

 very short, &c. There is no need to insulate 

 the preparation from the copper top of the 

 operation table ; the fur and skin offer 

 such resistance as makes that precaution 

 unnecessary. 



For observations with unipolar faradization, 

 cf. Alfred Frohlich and Sherrington (Jul 

 of Physiol, xxviii. 14 ; 1901), T. Graham 

 Brown and Sherrington {Quart. Jnl. of Exp. 

 Physiol, iv. 193; 1911), F. E. Miller {ibid. 

 vi. 68 ; 1913), A. F. S. Leyton and Sherring- 

 ton {iUd. xi. 135 ; 1917). 



For the limb movements dependent on 

 antidrome conduction down the root-fibres 

 of the dorsal columns see Sherrington, 

 'Antidrome Conduction in the Central 

 Nervous System' {Proc. Boy. Soc. vol. 61. 

 p. 243 ; 1897). 



