AND BLOOD PRESSURE 



177 



traction on the intestines is the most certain method of producing 

 fall of pressure. The shock produced by severe injuries or operations 

 is probably, therefore, of the same nature as collapse produced by 

 bleeding. In man after a severe 

 injury owing to the shock to the 

 sensory synapses, there is loss of 

 reflex tone, and relaxation of both 

 skeletal and vascular muscle. The 

 entire cessation of movement leads 

 to the pooling of blood in the peri- 

 pheral fields, and at the same time 

 the injury may entail considerable 

 loss of blood fluid. Toxic products 

 of altered metabolism probably arise 

 in the cooled and stagnant blood 

 which secondarily poison the ner- 

 vous system. Adrenalin and pitui- 

 tary extract by constricting the 

 arteries restore the blood pressure, 

 the former for a brief, the latter 

 for a much longer time (Mummery 

 and Symes). 



Chloroform, says Bayliss, con- 

 verts pressor into depressor reflexes 

 in the rabbit by reversing the usual 

 excitation of constrictors into inhibi- 

 tion. Strychnine, he says, converts 

 the inhibitory phase of all reflexes 

 into excitation ; thus the depressor 

 nerve produces a rise instead of the 

 usual fall under full doses of strych- 

 nine. The constrictor centre is ex- 

 cited by the mechanism which 

 normally inhibits it. The first 

 effect of a small dose in the normal 

 animal is to increase the action of 



Flo. 24. C, constrictor; D, 

 dilator neurones ; A, arterial 

 muscle cell of body ; K, of kidney ; 

 R, afferent nerve of kidney influenc- 

 ing bulbar and spinal centres as 

 shown by + and signs ( Bayliss). 



the vaso-constrictor centre on the viscera and dilate the cutaneous 

 vessels. The synapses of the pressor fibres with the constrictor 

 centre are the first to show paralysis as the dose is increased. 

 Thus the usual pressor effect which follows excitation of a sensory 



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