102(5 
DR. W. H. HASKELL ON THE RHYTHM OF THE HEART OF 
vagus produces no alteration in the size of the contractions, hut only an alteration of 
rhythm in accordance with the alteration of rate of the auricular contractions.'" 
Conclusion. 
The curves and arguments given in this paper show clearly that the vagus nerve 
exercises a powerful influence upon the muscular tissue of the heart as well as upon 
the motor ganglia. That it acts upon the muscular tissue is proved by the fact that 
its stimulation causes a profound alteration of the force of the muscular contractions, 
together with corresponding variations in the excitability and tonicity of the muscle, 
without necessarily altering the rate of rhythm. 
Its action upon the force of the contractions may be in the direction of diminution or 
of augmentation, so that the nerve sometimes causes a diminution of the force of the 
contractions followed by augmentation, sometimes augmentation alone without any 
previous diminution. 
This diminution may vary greatly both in extent and duration ; it may be very 
slight or so great that the contractions disappear altogether, so that in this way complete 
quiescence ma,y be caused ; it may be that the first few beats only after the beginning 
of the stimulation are affected or the effect may continue until some little time after 
the end of the stimulation. 
The extent of this diminution is in close connexion with the nutritive condition of 
the heart, so that quiescence followed by augmentation is more likely to occur when 
the heart is first suspended; and augmentation alone, without previous diminution, 
after the heart has been removed from the circulation for some time. 
Augmentation, therefore, without a previous diminution, is that effect of the stimu¬ 
lation of the vagus upon the muscular tissue which is the most enduring; and in 
accordance with this, poisons which gradually prevent the whole action of the vagus 
upon the muscular tissue always remove first the power of the nerve to cause a dimi¬ 
nution of the force of the contractions, and & fortiori quiescence, and afterwards its 
power to cause augmentation of that force. 
The vagus, also, in all probability acts upon the motor ganglia in the same direction 
as upon the muscular tissue. It is able at one time to cause slowing, at another 
acceleration without a previous slowing. The slowing is more likely to occur before 
removal of the heart, or immediately after the heart has been suspended ; acceleration 
alone or no effect at all after the removal of the circulation or after the heart has been 
suspended some time. 
So, too, poisons which entirely remove the action of the vagus first prevent the nerve 
from causing slowing, and only finally prevent the causation of acceleration. 
If, then, we compare slowing of the rate of the discharges from the motor ganglia to 
* N.B.—The hearts of Toads are apparently less susceptible to the action of all three of these poisons 
than those of Frogs. For instance, it takes much longer time to remove the whole effect of the action of 
the vagus by means of atropin (1 p. c. solution) in. the case of the former than in the case of the latter. 
