DISEASES OF THE HEART IN DOMESTIC ANIMALS. 
215 
resistance against stagnation is also aided by the valves lying in 
the veinous system. If circumstances occur in which stagnation 
of the blood in the right auricle ensues during the systole of the 
verticle,'for instance by an insuliicency of the tricuspid valves, the 
stagnation of the blood in the veins may become so significant 
that the rythmical expansion and contraction of the jugular veins 
is perceptible, a phenomenon which has been designated venous 
1)1 ood. The auricle being never entirely without blood during 
systole is noteworthy. Furthermore, the filling of the ventricle 
with blood is wholly independent of the varying pressure of blood 
in the veins. By means of the systole of the ventricle the blood 
contained therein receives an impetus to escape through both 
existing openings in each ventricle, but the moment after the 
systole of the ventricle, the auriculo-ventricular opening closes by 
means of the valves, the blood can flow into the pulmonary artery 
only, thus emptying the ventricle. The ventricle, however, does 
not remain entirely empty during the most violent systole. 
The auriculo-ventricular valves, the tricuspid of the right and 
the mitral valves of the ventricle are of particular importance. 
Their peculiar position at the opening of the ventricle, so that the 
blood flows between these and the walls of the ventricle, influences 
greatly the circulation and action of the heart upon the least 
deviation. 
As soon, however, as the pressure in the ventricle caused by the 
violent filling of blood, and through the influence of systole the 
walls of the ventricle contract, the auriculo-ventricular valves also 
begin to close completely. The completion of the heart’s action 
and the normal condition of the circulation depend particularly 
upon the precision with which the valves close. As is known, the 
valves act as a damper and must produce such a complete closure, 
so that not a drop of blood can flow from the ventricle into the 
auricle. 
At the commencement of the aorta and the pulmonary artery 
the semi-lunar valves prevent the return of blood through the 
arteries into the ventricle. These valves are applied against the 
walls by the penetration of the blood. However, in the begin¬ 
ning of the diastole of the ventricle the pressure of blood in the 
