438 Prof. C. S. Koy and Mr. J. G. Adami. [Feb. 11, 



number of facts showing that the vagus does lower the excitability of 

 the ventricles, and that, by means of muscarin and by discontinuous 

 stimulation of the vagus, it is possible to isolate the influence of the 

 vagus on the rhythm and force of the auricles from its influence 

 upon the excitability of the ventricles. The power of the vagus to 

 stop the ventricles temporarily can only be explained by this diminu- 

 tion of their excitability. 



We show that, with a certain degree of vagus excitation, irregu- 

 larity of the ventricles necessarily results, in consequence of the 

 sinus and the ideo-ventricular rhythms interfering with one another ; 

 that this is the common cause of irregularity ; and that irregularity 

 may also be caused by the auricles not responding to all the impulses 

 which reach them from the sinus. 



We explain that, in rare instances, direct excitation of the vagus 

 may so lower the excitability of the ventricle that the contractions 

 may not extend over the whole of their walls, and may in this way 

 produce the apparent weakening which is sometimes met with. 



In Section V we pass on to study the effect of direct excitation of 

 the nervi augmentores (acceler antes) upon the heart, and show that 

 the acceleration of the rhythm may be extremely slight if the heart 

 be beating fast, and that the acceleration and augmentation of force 

 of the heart bear no constant proportion to one another. The 

 augmentor nerves increase the diastolic expansion of the auricles and 

 also increase their systolic contraction ; but these two effects do not 

 go hand in hand. 



Excitation of the augmentors increases the output of the heart, 

 owing to the increased force and frequence of the auricular contrac- 

 tions, the result of this being that the pressures in the systemic and 

 pulmonary arteries rise, while the systemic and pulmonary venous 

 pressures fall. If there be but little quickening, the contraction 

 volume of the ventricles is increased. 



The augmentors, on direct stimulation, cause a slight increase in 

 the diastolic expansion of the ventricles, which is passive in nature 

 and due to the increased force of the auricular contraction. The 

 force of the ventricular contractions is increased ; they contract more 

 completely, diminishing the amount of residual blood, in spite of the 

 fact that the arterial pressure is usually somewhat raised. 



There are certain nerve fibres other than the nervi augmentores 

 proper which pass from the stellate ganglion to the heart, some- 

 times by the annulus of Vieussens to the inferior cervical ganglion, 

 but sometimes as separate branches passing directly to the heart 

 from the ganglion stellatum, or the annulus. On peripheral excita- 

 tion of the cut nerves there is marked weakening of the contractions 

 both of the auricles and of the ventricles, usually with some degree 

 of slowing, this being sometimes followed on cessation of the excita- 



