142 DISEASES OF THE CIRCULATORY APPARATUS. 



some diseases of the heart (incompensated valvular defects, myo- 

 carditis), after large doses of digitalis, aud ia heart-weakness. It 

 is only intermittent (as a forerunner of entire irregularity) in 

 slio-ht cases of valvular defects, in some diseases of the brain, 

 and in gastrocism. The pulse is full and distended where great 

 physical exertion is used; small and collapsed after severe hem- 

 orrhage and in enteritis. In intense heart-weakness and collapse 

 it becomes thread-like and imperceptible. 



The venous pulse — that is, the apparent increase in the amount 

 of blood in the jugular at its entrance into the chest — is often seen 

 in the dog. It is generally a symptom of some chronic heart- 

 affection, such as imperfect closing of the tricuspid valves, and of 

 heart-weakness. 



DISEASES OF THE HEART. 



Valvular Defects. 



General Notes on Valvular Defects. By valvular 

 defects we understand such anatomical alterations in the valves and 

 openings as lead to an irregularity in the circulation of the blood, 

 becoming apparent by visible symptoms in the pulse "or general 

 condition; but those slight valvular defects so often seen in po:?t- 

 mortems and never noticed during life, are not to be considered. 



Valvular defects appear in two forms: first, when the valves 

 close imperfectly ; or, secondly, when the openings become con- 

 tracted, causing stenosis. Imperfect closure of one valve causes a 

 certain amount of blood to flow back into the portion of the heart 

 from whch it has just come; for instance, when we have imper- 

 fect action of the mitrals or of the tricuspids in systole, part of 

 the contents of the ventricles run back into the auricle, and when 

 there is insufficient action of the semilunar valve in the diastole 

 a part of the blood that has been thrown into the artery returns 

 into the chamber again. 



Stenosis of one opening retards the passage of blood, when we 

 have a contraction of an arterlo-ventricular opening. At the time 

 of diastole the blood is kept back at the entrance of the affected 

 ventricle, and it is imperfectly filled; while in the aortic opening 

 in pulmonic stenosis the exit of the blood out of the ventricles 

 (Fig. 40) in systole is retarded. In any of these conditions there 



