Studies from the Dept. of Physiology Volume 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 Excerpt: ...above show that in order to obtain either reflex inhibition or reflex excitation of the cardio-inhibitory centre it is necessary that this centre be in a condition of unstable equilibrium; if the centre is in this condition, the result of stimulating a sensory nerve is determined in part (but only in part, as will be shown later) by the rate at which the heart is beating when the nerve is stimulated: if the heart is beating slowly, reflex acceleration results; if it is beating rapidly, reflex slowing occurs. Thus, in one of many experiments the heart rate was 24 in 10 seconds, and stimulation of the saphenous nerve caused the heart rate to decrease to I.." A small amount of warm normal saline solution was injected into the femoral vein, as a result of which the heart rate decreased to 18 in 10 seconds; stimulation of the saphenous now caused the rate to increase to 26 beats, but after the stimulation it returned to 18. Repeated stimulation, or sometimes a single stimulation of a sensory nerve, tends to cause permanent (, . e. permanent for the individual experiment) changes in the heart rate. Thus, if the heart is beating slowly, two or three stimulations of a sensory nerve may cause an acceleration of the heart which continues for hours, or as long as the experiment continues; simply ligating the sciatic nerve has caused a similar effect. If, on the other hand, the heart is beating rapidly, repeated stimulations may cause the rate to become and remain slow. These are further illustrations of the already mentioned tendency of the heart to reach and remain at a constant rate, whenever its rate has been changed. The afferent nerve fibres by-which reflex acceleration is produced.--Attention has already been called to the part which the condition of the car...