THE CIRCULATION OF THE BLOOD AND LYMPH 141 



view that the cells on the course of nerve-fibres in the heart 

 are rather stations where the fibres lose their medulla, and 

 where possibly other anatomical changes and rearrangements 

 occur, than important intermediate mechanisms which 

 essentially modify the physiological impulses falling into 

 them, and shape the visible results that follow those im- 

 pulses. In the discussions that have arisen over this 

 question, 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 aug- 

 mentation. But stimulation of the junction of the sinus 

 and auricle still causes inhibition, as in the normal heart. 

 Curara, conine, and other drugs, resemble nicotine in this 

 respect. 



Atropia and its allies, such as daturine, not only abolish 

 the inhibitory effect of stimulation of the vagus trunk, but 

 also that of stimulation of the junction of sinus and auricle. 



Muscarine, a poison contained in certain mushrooms 

 (p. 174), causes diastolic arrest of the heart, which, when 

 the circulation is intact, becomes 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 atropia or its allies. And a heart 

 brought to standstill by muscarine can be made to beat again 

 by the application of atropia, 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 atropia group paralyzes 

 the nerve-endings themselves, 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 some other local nervous mechanism, and thus 



