PEACTICAL CONDUCT OF EXERCISE V 143 



section ; (3) the observation can, by simply shifting the stigmatic electrode, be extended to 

 the provocation of localized reflex movements in ipsilateral fore-limb or hind-limb as desired. 

 These latter demonstrate antidrome conduction down the dorsal white column. 



It is noteworthy that although moderate faradization of the face of the lateral column at 

 top of the cord so readily gives vasopressor reaction in the decapitate preparation, faradiza- 

 tion, even pushed to extreme, of an afferent limb-nerve, e. g. sciatic, as a rule quite fails. Very 

 occasionally is any ejBfect obtained. The experiment as repeated by my class, some 80 times 

 in the last six years, has yielded clear reflex effect on the arterial pressure only twice — in 

 both instances a rise, but not of large extent. In the spinal mammal when transection- 

 shock has passed off, e. g. some weeks after the transection, large rises of art. pressure on 

 faradization of afferent limb-nerves are easily obtained. 



EXERCISE VI 



Obs. 23. The observation as arranged in the student's instructions relieves the asphyxia 

 before the onset of convulsive movements of the skeletal musculature. It can of course be 

 carried further than so arranged ; in that case the student should understand that the a. p. 

 record becomes complicated by mechanical effects from the contracting muscles ; there is, 

 moreover, then a risk that the movements of the neck-stump may detach the carotid cannula 

 from the junctional tube to manometer. But the asphyxial effect, even when pushed to 

 produce general convulsions, can be recovered from by resuming the chest ventilation, and a 

 fair circulatory condition re-established although the heart-beat under the prolonged asphyxia 

 had become extremely slow and feeble. 



Obs. 25. Students find more difficulty in inserting a cannula into a vein than into an 

 artery. 



Obs. 26. Entomological pins, silvered or gilt, sizes 18, 19, serve excellently. They 

 also make good hand-electrode tips, and good tips for vibrating spring contacts in Hg pools. 



EXERCISE VII 



For this operation the student gets much help from the mounted skeleton (see p. 130) 

 laid on its left side in the operative position. The splanchnic effect seems particularly 

 marked in the adult male in the breeding season. 



Obs. 27. This is omitted from a first performance of the exercise because (1) it involves 

 severance of the nerve midway in its course, tending to leave stumps somewhat difficult and 

 short for clean stimulation ; (2) considerable reflex movement may accompany the 

 stimulation of the central stump, making difficult the holding in place of the electrode 

 during stimulation. The stimulation is best done by unipolar faradization, the end of the 

 single-wire electrode being bent into a little loop through which the nerve is lightly drawn 

 by its attached ligature. The rise of a. p. evoked by stimulation of central end of splanchnic 

 nerve is, so far as I am aware, the only evidence usually obtainable from the freshly severed 

 spinal cord of the existence of spinal vasomotor centres, unless direct faradization of cord 

 and the rise in asphyxia be accepted as such. The somatic nerves, e. g. central sciatic, very 

 rarely evoke any perceptible vasomotor reflex, although later, i. e. when cord has been 

 severed for weeks or months, they do so readily (Sherrington, Integrat Action of the Nervous 

 System, p. 242, 1906). 



