PATHOLOGICAL DISTURBANCE OF FUNCTION OF HEART. 99 



vessels, the semilunar valves are opened, become stretched like tendon 

 above their concave sinuses (Fig. 24), without becoming applied to the 

 arterial wall, and allow the blood to enter. 



Goltz and Gaule found, by means of maximal and minimal manometers, a 

 negative pressure in the ventricles during a certain phase of the heart's con- 

 traction amounting in the dog to 23.5 mm. of mercury in the left ventricle. 

 They suspected that this phase coincided with the diastolic dilatation and for 

 which they thus assumed a considerable power of aspiration. Moens is of the 

 opinion that this negative pressure prevails in the ventricle shortly before the 

 systole has reached its maximum. He explains the aspiration as being produced 

 by the formation of a vacuum in the ventricle, which must develop as a result of 

 the active movement of the blood, through the aorta and the pulmonary artery, 

 behind the circulating mass of blood, therefore in the ventricle. Gaule and Mink 

 believe that the systolic enlargement of the aorta must at the same time cause a 

 dilatation of the conus arteriosus of the left ventricle. 



(D) After the ventricular contraction has attained its height and 

 relaxation has commenced, the semilunar valves close with an audible 

 sound (Fig. 27). The diastole of the ventricle is followed by the pause. 

 Under normal conditions the two halves of the heart contract and relax 

 simultaneously and uniformly. 



The heart-muscle exhibits in its activity certain variations in tone, that is, 

 it does not with every systole contract from the same degree of relaxation to 

 the same degree of contraction, but, rather, there follow in rhythmical periods 

 series of contractions that arise from a considerable 

 degree of relaxation of the heart-muscle, alternating 

 with series of contractions that begin in a less com- 

 plete degree of relaxation. With the latter the degree 

 of contraction is greater than with the former. These 

 variations in tone have been found especially in the 

 auricle of the tortoise-heart. When the arterial blood- 

 pressure is moderately increased, the heart expels a 

 larger amount of blood; if, however, the arterial 

 pressure is greatly increased, the amount of blood 

 expelled at each systole becomes less. Extracts of 

 testicle, suprarenal gland, pituitary gland and spleen 

 in 0.7 per cent, sodium-chlorid solution added to blood 

 exert a tonic effect upon the heart; the extent of the 

 contractions increases and the beats become more 

 regular. Under the influence of alcohol the heart FIG. 27. The Closed Pulmonary 

 exhibits a marked degree of relaxation and a low v^'i 11 ^ Valv f s * Man 



degree of contraction. The influence of various poi- 

 sons is variable. Heat increases the variations in tone. 



Whether the relaxation of the heart-muscle is an active dilatation or not has 

 been decided in the affirmative by some investigators. Stimulation of the vagus 

 (likewise digitalis and strychnin) is said to increase the active dilatation; 

 while section of the vagus (likewise atropin) is said to diminish it. 



PATHOLOGICAL DISTURBANCE OF THE FUNCTION OF THE 



HEART. 



All obstructions to the blood-flow through the different portions of the heart 

 or of the vessels connecting them give rise to a permanent increase in the work 

 of that portion of the heart especially concerned with relation to the affected 

 section of the circulation, and in consequence to an increase in the thickness of 

 the muscular walls, with dilatation of the cavity. Should the resistance affect not 

 alone one section of the heart, but consecutively other parts further on in the 

 course of the blood-stream, these also will undergo secondary hypertrophy. If, 

 in addition to increasing the muscle-substance of the affected portion of the heart, 

 its cavity is at the same time dilated, as is often the case, the condition is designated 

 excentric hypertrophy, or hypertrophy with dilatation. 



The obstructions under consideration in the domain of the vascular channels 

 are: constriction (stenosis) of the arterial 1 or venous orifipes arid likewise defective 



