Page:The Harveian Oration,1902.djvu/39

31 centres are all closely inter-related to each other. Of these the respiratory is most readily influenced, both from the periphery and the higher centres, and it is not improbable that many of the variations in cardiac rhythm and vascular tone so induced are in reality conditioned only mediately through the respiration. With the exception of the depressor and the nerves of the air passages and lungs, moderate stimulation of perhaps all other sensory nerves, general and special, causes constriction of the blood-vessels, with a rise of blood pressure and acceleration of the heart. This, however, is a rule liable to many exceptions, the conditions of which are not as yet in all respects satisfactorily determined.

In states of exhaustion, and when the stimulation is of a sudden or intense character, more particularly when of visceral origin, there is a fall in blood pressure and reflex inhibition of the heart, which, in certain conditions, may be fatal. As an instance of this kind one may quote Goltz's famous "Klopfversuch," by which it is shown that a smart tap on the abdomen of a frog causes stoppage of the heart and dilatation of the splanchnic blood-