CIRCULATION. 161 



The connection of the extrinsic cardiac nerves with the intracardiac mus- 

 cle and nerve-cells is not yet determined satisfactorily. ( lertain fibres in the 

 vagus, said to be derived from the spinal accessory nerve, terminate in " end- 

 baskets" embracing sympathetic ganglion-cells, the axis-cylinder processes 

 of which end on the cardiac muscle-fibres. Probably the inhibitory action 

 of the vagus is exercised through these cells, as it is lost in animals poisoned 

 with nicotine, which is known to paralyze, in other situations, either the end- 

 baskets about sympathetic cells or the body of the cell itself. Other vagus 

 fibres apparently terminate (or arise) in an end-brush in the pericardium and 

 endocardium. 



The augmentor apparatus consists of two, possibly three, neurons. The 

 cell-body of one lies in the spinal cord ; its axis-cylinder process leaves the 

 cord in the white ramus and terminates in a ganglion of the sympathetic chain 

 (inferior cervical, stellate ganglion). The axis-cylinder process of the sympa- 

 thetic ganglion-cell passes directly to the cardiac muscle-fibre on which it 

 ends, or, possibly, terminates in physiological contact with the dendrites of a 

 third neuron lying in the heart, the neuraxon of which carries the augment- 

 ing impulse to the muscle-cell. Stimulation of the white ramus causes aug- 

 mentor effects. In nicotine-poisoning, these effects cannot be obtained ; but 

 stimulation on the distal side — the cardiac side — of the cell-body about which 

 the neuraxon ends, still causes augmentation. If nicotine paralyzes the 

 sympathetic cell-body, this experiment proves that there is no cell in this 

 neuron chain between the point stimulated and the muscle-fibre ; if it par- 

 alyzes the end-basket and not the cell-body, the existence of the third (intra- 

 cardiac) neuron in the chain is possible, provided the communication between 

 the second and the third neuron is not by means of an end-basket ; but, as 

 Dogiel and Huber assume, by a contact with the dendrites, similar to that 

 observed by them in other sympathetic cells, and not sensitive to nicotine. 



The Inhibitory Nerves. 



In 1845, Ernst Heinrich and Eduard Weber announced that stimulation 

 of the vagus nerves or the parts of the brain where they arise slows the heart 

 even to arrest. When one pole of an induction apparatus was placed in the 

 nasal cavity of a frog and the other on the spinal cord at the fourth or fifth 

 vertebra, the heart was completely arrested after one or two pulsations and 

 remained motionless several seconds after the interruption of the current. 

 During the arrest, the heart was relaxed and filled gradually with blood. 

 When the stimulus was continued many seconds, the heart began to beat again, 

 at first weakly and with long intervals, then more strongly and frequently, 

 until at length the beats were as vigorous and as frequent as before, though all 

 this time the stimulation was uninterrupted. 



In order to determine from what part of the brain this influence proceed-, 

 the electrodes were brought very near together and placed upon the cerebral 

 hemispheres. The movements of the hear! were not affected. Negative results 

 followed also the stimulation of the spinal cord. Not until the medulla oblon- 



VOL. I.— 11 



