HEART 



605 



lik-- (xnniliuntr) valves, which prevent backllow 

 f i om vessels to ventricles. 



When the heart is at work, tlie simultaneous con 

 I r.i< lion of the two auricles ( i.e. of the muscle til. res 

 on their \\all-i is followed l.\ a similar contraction 

 >i tint ventricles, and this l>y a pause or passive 

 interval of re expansion, after which the rhythm 

 <>l contraction recommences. In the contraction of 

 the auricles, ihe mass of hlood in the large veins 

 will not permit of a hackllow in a peripheral direc- 

 tion, so that virtually all the contents of the 

 auricles pass into tlie respective ventricles, which 

 at I hat moment are llaccid ami uncontrao.ted. As 

 the ventricles fill, the valves between them and the 

 auricles are partly closed, and this is perfectly 

 Accomplished when tlie contraction of the ventricle 



sets in. As 

 no blood can 

 then pass back 

 from ventricle 

 to auricle, the 

 energy of ven- 

 tricular con- 

 ^ traction is 



directed to 

 overcoming 

 the resistance 

 of the semi- 

 lunar valves 

 guarding the 

 entrance to 

 the pulmon- 

 ary artery and 

 the aorta, 

 which are 

 Pig. 2. -Diagram of Heart halved and m oreov e r 

 laid open ( after Debierre ) : 



A, B, C, D, as in flg. 1. a, part of tricuspid 





 11 



, , , , . . , 



valve ; 6, part of mitral ; c, setnilunars at The state of 

 base of pulmonary anery. a', a', inferior contraction in 

 and superior venae cavas entering A ; &',&', o.j^pip or vpn 

 pulmonary arteries proceeding from B; ~. 

 <t,<J, aorta proceeding Irom C ; d',d', pul- tricle 18 called 

 monary veins entering D. the systole ; 



the state of 



passive relaxation and expansion the diastole, 

 and it is evident that bv the systole of the 

 auricles the ventricles are filled, and that by the 

 systole of the ventricles their contents are for the 

 most part forced into the arterial systems of lungs 

 and body. As the heart usually beats about 

 seventy-two times a minute, the cycle of events 

 just noted lasts about fyths of a second, of which 

 tin- systole of the ventricle lasts about ^ 5 ths, that 

 of the auricle perhaps ^th, and the passive interval 

 about T* ths of a second. 



The activity of the heart has several external 

 indices, such as the beating, seen and felt between 

 the Of th and sixth rib on the left side, due to con- 

 traction of the ventricles, which makes the ' apex ' 

 of the heart strike against the pericardium, and 

 through this on the wall of the chest. There are 

 also sounds produced by tlie heart : (a) the longish 

 dull sound probably caused by the contraction of 

 the muscular Obres of the ventricles and the ten- 

 sion of the valves between these chambers and the 

 auricle; (b) the sharp sound due to the sudden 

 closure of the semilumir valves when the contrac- 

 tion of the ventricles ceases. The heart sounds 

 are of great importance in the diagnosis of disease 

 of the heart. They may undergo various changes 

 and may in some cases disappear or be replaced by 

 or accompanied by murmurs. These murmurs are 

 caused by the blood (lowing through the orifices of 

 the heart which have become changed by disease. 

 At a distance from the heart, the pulse or regular 

 dilatation of an elastic artery is a familiar index. 

 The heart is under the control of three sets of 

 nerves : ( u ) from ganglia in its own substance, 



essential to the regular rhythm of con- 

 traction ; (It) from the sympathetic system, appar- 

 ently affect ing rapidity of action ; (c) from tlie 

 pncumogastric or vagus nerve, coming directly 

 from the brain, apparently with arresting power. 

 See AORTA, AKTKKIKS, BLOOD, CIRCULATION ; 

 text-books of Anatomy by Quain, Turner, Mivart, 

 Macalister, &c. ; of Physiology by Foster, Huxley, 

 Landois and Stirling, &c. 



DISEASES OF THE HEAKT are either those affect- 

 ing the various tissues consuming the heart, or the 

 nervous arrangements governing the heart. 



( 1 ) Diseases of Structures composing Heart may 

 be primary or secondary. 



(a) Primary Diseases. All the various tissues of 

 the iieart may be primarily affected. The Peri- 

 cardium (sac surrounding heart) may be affected 

 with inflammation (pcrtca&Ktis). This is by no 

 means an uncommon condition in rheumatic fever, 

 while it also occurs in connection with some of the 

 acute exanthemata. Fluid tends to be effused into 

 the sac, and this produces great impairment of the 

 heart's action. The condition frequently leads to a 

 fatal termination. Various tumours may occur in 

 connection with the pericardium. 



The Myocardium (muscular wall of heart) may 

 also be affected with inflammation leading to very 

 irregular and impaired action of the heart, and 

 often to death. This is known as myocarditis, and 

 if the fatal termination does not ensue in the acute 

 stage of the disease, the wall of the heart is apt to 

 be left in a weakened condition due to the patho- 

 logical changes set up in the course of the inflam- 

 mation. The myocardium may occasionally be the 

 seat of tumours. The muscular substance of the 

 heart may undergo a fatty degeneration, which 

 may produce death either from failure of the heart, 

 or more rarely by rupture of the wall. 



The Endocardium ( lining membrane of heart ; 

 also forms the valves of the heart) is the most 

 common seat of inflammation in rheumatic sub- 

 ject* and in individuals suffering from scarlet fever 

 or from some other of the exanthemata. This 

 endocarditis is specially apt to attack the valves of 

 the left side of the heart, and to lead to deformity 

 and the imperfect action of these important struc- 

 tures. When this occurs the well-known train of 

 symptoms commonly associated with heart disease 

 are apt to appear breathlessness, palpitations, 

 irregular heart s action, dropsy, albuminuria, &c. ; 

 while the various signs of valvular disease, among 

 the most important of which is the alteration in the 

 sounds of the heart, and the development of mur- 

 murs may also be determined. In many cases, 

 however, in spite of disease of the valves, the heart 

 may continue to act satisfactorily. But there is 

 always a great danger of its proving inadequate to 

 the additional work thus put upon it, and of its 

 suddenly failing under any extra strain. 



There is one peculiar form of inflammation of the 

 endocardium known as acute ulceratire endocarditis 

 which is exceedingly fatal, and which is due to the 

 development of micro-organisms in the heart. 

 Certain slow degenerative changes may also affect 

 the endocardium, more especially where it com 

 poses the aortic valves (Atheroma). 



In all inflammatory affections of the heart there 

 is a tendency for all the structures to be involve*! 

 at one and the same time. 



(b) Secondary Diseases. As the result of various 

 morbid states of other parts of tlie body, the heart, 

 and more especially its muscular wall, may 

 become secondarily affected. Thus in fever the 

 muscular snltance of the heart manifests the con- 

 dition of cloudy swelling, and thus becoming weak- 

 ened tends to yield to the pressure of blood inside 

 the heart, and to undergo dilatation. This state of 

 the organ is frequently accompanied by the develop- 



