1 64 THE CIRCULATION OF THE BLOOD AND LYMPH 



tricular node, the upper end of the A-V bundle, the main conduction 

 system (Cohn and Lewis). 



The nervi accelerantes are already non-medullated before they 

 reach the heart. The fact that the action of the accelerantes can 

 be restored by perfusing the heart with a nutrient solution at a 

 much longer interval after somatic death than the action of the 

 vagus strengthens the suggestion that ganglion-cells are interposed 

 on the inhibitory though not on the augmentor path, without, 

 however, proving of itself that such a difference exists. In one 

 experiment the heart of an anthropoid ape was revived when three 

 successive periods viz., four and a half, twenty-eight and a half, 

 and fifty-three hours respectively had elapsed after the death of 

 the animal, although during the last period the heart had been 

 twice frozen hard. The vagus was shown to be still capable of 

 causing some inhibition six hours after death, and the accelerans 

 some augmentation as late as fifty-three hours after death (Hering). 



In the discussions that have arisen over the relation of the extrinsic 

 to the intrinsic cardiac nervous apparatus appeal has frequently been 

 made to the action of certain poisons on the heart. 



Thus, after nicotine has been injected subcutaneously, or painted 

 directly on the heart of a frog, stimulation of the vago-sympathetic 

 causes no inhibition; it may cause augmentation. But stimulation of 

 the junction of the sinus and auricle still causes inhibition, as in the 

 normal heart. 



Atropine and its allies, such as daturine, not only abolish the inhibi- 

 tory effect of stimulation of the vagus trunk, but also that of stimula- 

 tion of the junction of sinus and auricle. 



Muscarine, a poison contained in certain mushrooms (p. 197), causes 

 diastolic arrest of the heart, which, when the circulation is intact, be- 

 comes swollen and engorged with blood. This action takes place in a 

 heart already poisoned with nicotine or one of its congeners, but not in 

 a heart under the influence of atropine or its allies. And a heart brought 

 to a standstill by muscarine can be made to beat again by the applica- 

 tion of atropine, although not by nicotine. 



These facts may be explained as follows : Nicotine paralyzes, not the 

 very ends of the vagus, but the ganglia through which its fibres pass. 

 Stimulation of the sinus, which is practically stimulation of the vagus 

 fibres between the ganglion-cells and the muscular fibres, is therefore 

 effective, although stimulation of the nerve-trunk is not (Langley). 

 On the other hand, the atropine group paralyzes the nerve-endings 

 themselves, or interferes with the reception of the inhibitory impulses 

 by acting on a so-called receptive substance in the muscle (p. 180), so 

 that neither stimulation of the sinus nor of the nerve-trunk can cause 

 inhibition. Muscarine, on the contrary, stimulates the vagus fibres 

 between the nerve-cells and the muscle, or the actual nerve-endings, or 

 exerts an inhibitory action on the muscle itself through the appropriate 

 receptive substance, and thus keeps the heart in a state of permanent 

 inhibition, which is removed when atropine cuts out the nerve-endings, 

 or combines with the receptive substance. It is quite in accordance 

 with this that muscarine has no effect on a heart whose vagus nerves, 

 as occasionally happens, have no inhibitory power. Pilocarpine has 

 very much the same action as muscarine. 



The view that muscarine and atropine can directly affect the cardiac 



