APPLIED PHYSIOLOGY 



great overdistension of the right heart in asphyxia may 

 help to explain the emptiness of the left. 



There is probably but little room for lateral movement 

 of the heart inside the pericardium. The change in 

 position of the apex-beat when an individual moves over 

 on to his side a change which may amount to some 

 inches is believed by physiologists to be due to the 

 heart rolling over inside the pericardium under the 

 action of gravity, so that a different part of its wall 

 comes into contact with the chest. It is doubtful, how- 

 ever, if this can be regarded as a complete explanation, 

 for ' fixation of the apex-beat ' is believed by many good 

 clinical observers only to occur when the pericardium 

 itself is adherent to the chest wall, but not when the 

 heart and pericardium are alone adherent to one 

 another. 



The Valvular Mechanism of the Heart. 



If the blood contained in the heart is always to be 

 driven on in a definite direction, it is obvious that the 

 orifices between its different chambers and at its entrances 

 and exits must be provided with valves. The tendency 

 amongst clinicians in the past a tendency due partly to 

 the introduction of the stethoscope as an instrument of 

 observation and partly to an almost exclusive study of 

 the naked- eye pathology of the heart has been to attach 

 an undue importance to the membranous valves as 

 guardians of the orifices. At all events, this is in- 

 disputably true as regards the auriculo- ventricular 

 valves. It is doubtful, as MacAlister has said,* if these 

 * Brit. Med. Journ., 1882, ii. 821. 



