752 DR FRASER ON THE PHYSIOLOGICAL ACTION 



These are sufficient to prove that Calabar bean influences the heart neither by 

 an action on the inhibitory centres nor by one on the nerves that connect those 

 centres with it. I think they are also sufficient to exclude the rest of the cerebro- 

 spinal nervous system : as the only other spinal nerves connected with the heart, 

 by the branches of the great sympathetic trunks or otherwise, are either sensory, or 

 at any rate afferent, nerves that form through the cord reflex arrangements with 

 the vagi and vaso-motor nerves ; or excito-motory ones whose action is to increase 

 the frequency of the heart's contractions, but whose function is only periodically 

 exerted, and is quite unnecessary for the continuance of the ordinary rhythmical 

 occurrence of those contractions.* But, to remove the possibility of any doubt 

 on this point, the following experiment was performed :— 



Experiment LV. 



The spinal cord was divided between the occiput and first vertebra of a frog, weighing 376 

 grains, and a wire was passed down the spinal canal, so as to produce complete paralysis, and 

 into the cranial cavity, so as thoroughly to break up and destroy the brain. A short time there- 

 after, the heart was contracting at the rate of forty beats per minute. One half of three grains of 

 extract, in twenty minims of water, was injected into each thigh. 



2 minutes afterwards, cardiac contractions = 37 per min. 

 4 „ „ = 31 



6 „ „ =28 „ 



8 „ „ =26 „ 



10 „ „ = 25 „ 



12 „ „ =24 „ 



14 = 9 2 



16 „ „ = 20 „ 



18 „ „ = 17 „ 



20 „ „ = 14 „ 



22 „ „ -13 „ 



24 .., „ = 12 „ 



* Dr Power observes, in the sixth edition of Carpenter's " Principles of Human Physiology " 

 (page 217, note), that " the essential cause of the rhythmical action of the heart must still remain 

 an unsolved question." The exact influence of the various nerves that connect the heart with the cen- 

 tral nervous systems, appears to be quite as imperfectly ascertained, judging by the contradictory state- 

 ments and deductions of eminent physiologists. Legallois and Philip Wilson, and, afterwards, Budge, 

 Schiff, Reid, Weber, Moleschott, Von Bezold and others, have shown that a connection certainly 

 exists ; but they have left the details of the question unsettled by the great differences in many of 

 their opinions, as, for example, on the cardiac functions of the vagi. Von Bezold, in 1863, 

 attempted to prove the existence, in the spinal cord, of an excito-motory centre, whose stimulation 

 increases not only the number of the beats, but also the blood- pressure — the latter being due to 

 augmented force in the heart's contractions. Ludwig and Thiry opposed this opinion, and asserted 

 that the increased blood-tension is really an effect of excitation of the vaso-motor nerves. In a 

 recent investigation (Comptes Rendus, 25 Mars 1867), MM E. and M. Cyon give their adherence 

 to the views of Ludwig and Thiry. They also attempt to show that the spinal cord, through the 

 sympathetic system, supplies the heart with nerves that possess the power of directly accelerating its 

 contractions, and that are antagonistic to the vagi, in that, while the latter diminish the frequency 

 and increase the force of the contractions, the spinal " nerfs accelerateurs," on the other hand, 

 increase the frequency and diminish the force. — April 1867. 



