1058 Inteniiitk'iit Hfart Action. 



Etiology. The omission of ventricular contractions occurs 

 frequently in horses as a sequel of acute infectious diseases 

 especially in the course, or during the conyalescence, of in- 

 fluenza ; in other animals it is hardly ever observed. As the 

 actual cause a reflex or immediate excessive stimulation of the 

 X. vagus may be assumed, since in the cases observed l)y the 

 author the omissions could always be relieved by atropine, 

 which is known to paralyze the vagus endings. The stinuda- 

 tiou of the vagus becomes manifest by the intermediation of 

 the central nervous system when the omissions occur in brain 

 affections, for instance, in case of increased intracranial pres- 

 sure (chronic Hydrocephalus internus, brain tumors, inflam- 

 mation of the brain coverings, etc.). Digestive disturbances 

 (enteric catarrh, obstipation) also sometimes give rise to 

 transitory intermissions ^vhicll are probably produced by 

 chemical substances that have been absorbed from the intestine, 

 in such a manner that the poisons irritate the X. vagus or its 

 center either directly or reflexly. The ventricular systole may 

 Anally be omitted in certain cases in connection with diseases 

 of the heart muscle or of its nervous apparatus, for instance, 

 in acute inflammatory processes in the heart muscle, in the 

 pericardium or in the endocardium. 



Intermissions of the heart beat which are produced by 

 additional systolic contractions occur in all animal species and 

 always depend upon an abnormal stimulation of the heart. 

 The abnormal stimulation consists either in an increased 

 diastolic pressure in any one portion of the heart (in heart 

 weakness), or it develops in acute inflammatory processes in 

 the heart muscle, in the pericardium or endocardium. Some- 

 thnes poisons which have been al)sorbed in the intestines exert 

 an abnormal stimulation upon the heart. 



Pathogenesis. The physiological irritability or conductivity 

 of the heart is reduced by excessive stimulation of the X. vagus, 

 and this occurs first on the points of transition between the 

 auricles and the ventricles, where the compartments of the 

 heart are connected only Ijy small muscular bundles. In con- 

 sequence single contractions of the heart muscle omit, according 

 to the degree of disturbance either only in the ventricles or 

 also in the auricles. The same occurs in diseases of the heart. 



Under the influence of an abnormal stimulation at the time 

 when the respective heart segments are usually in diastole, 

 an unusual contraction, an additional systole occurs following 

 immediately upon a normal systole but preventing the oceur- 

 i-ence of the next normal systole by reducing the irritability 

 of the heart for a time. The sooner the additional systole 

 follows upon the immediately preceding normal contraction, the 

 less complete are the filling and contraction of the heart, the 

 aortic pressure being as yet lowered but slightly, and in con- 



