The exact site of the apex-beat of the heart should be always ascer tained, as this may be greatly influenced by disease in the chest cavity. In young children and infants the normal position of the heart's apex is nearer to the left nipple than is the case in the adult. This is partly due to the position of the nipple, which is placed relatively lower than it is in later life. In many children, instead of lying over the fourth rib it is in the fourth interspace or on the upper border of the fifth rib. But in addi tion to the lower position of the nipple, the heart itself is smaller• or seems to lie higher in children, espeCially during the period of infancy..
Often the apex will be found to beat in the fourth interspace, exactly on the site of the nipple.
Diseases of the heart-walls of course influence considerably the position of the apex-beat ; but when the organ is healthy, the position of its apex may be altered by morbid conditions in neighbouring parts. Effusion into the chest cavity causes displacement of the heart's apex. According to the side affected the heart may be pushed considerably to the right or to the left. In cases of left pleurisy with copious effusion it is not uncommon to find the apex-beat of the heart in the epigastrium, and sometimes the im pulse can be felt to the right of the sternum. Cardiac displacement does not, however, always result from effusion into the pleura ; and therefore its absence must not be taken to indicate that the physical signs are capable of another interpretation. If adhesions have formed between the pericar dium and the left pleura, the heart is held in place and cannot be pushed aside by the effusion. The position of the heart may be also altered by contraction of the lung on one side, but in this case the heart is drawn towards the affected part. In fibroid induration of the lung, disease on the right side moves the heart to the right ; disease on the left side draws the organ upwards and to the left.' Besides the position of the heart the exact level of the liver and spleen should be noted, as the position of these organs may help us to a conclu sion in a doubtful case. These viscera are often sensibly displaced by the pressure of a liquid effusion in the chest, while displacement of the liver by the bulging of a croupous pneumonia is so rare as to be a clinical curi osity. If the lung be contracted, the liver or spleen is drawn upwards into the chest.
Percussion of the chest in the infant and young child should be con ducted with deliberation. If care be taken that the hands are perfectly warm, and that undue violence is avoided, the process seldom arouses any special opposition. It is sometimes recommended to reverse the ordinary arrangement and practise auscultation before employing percussion, but this inversion of the customary rule is at least unnecessary.
In the young subject, except perhaps in the new-born infant, the re sonance of the chest is greater than it is in after-life ; and the percussion note obtained over an area of consolidation is often so modified by reson ance from healthy tissue around that dulness is only imperfectly marked and may escape the notice of an unpractised ear. Percussion should be mediate ; and it is advisable always to use two fingers in striking the fin ger placed upon the chest-wall. By this means, without employing undue force, a larger body of sound is elicited than if the chest is struck with one finger only, and dulness, if present, can be more readily appreciated. As we proceed we must be careful to make constant comparison between dif ferent parts of the chest—between opposite sides, between the base and the apex, etc. To make the comparison an accurate one the same period of the respiratory movement should be chosen for striking upon the finger ; for if one part of the chest be percussed at the end of an inspiration, and another at the end of an expiration, the difference even in a healthy chest may be considerable. When the consolidation consists in scattered no dules, as in the beginning of catarrhal pneumonia or in lobular collapse, dulness, which escapes the ear when percussion is made in the ordinary manner may often be detected by using "broad percussion," i.e., by strik in with three fingers upon three fingers placed upon the chest-wall as plex imeters. By this means the sound is collected from a larger area of lung tissue than if one finger only were employed.
But besides the character of the sound elicited in percussion, it is im portant to attend to the degree of resistance of the chest-wall. The resist ance to the percussing finger varies greatly in different cases and is a sign of no little importance. In the consolidation of pneumonia and in that of pulmonary atelectasis, when the collapse occupies only a superficial layer of tissue, resistance is slight. In more extensive collapse, as when the con densed tissue embraces an entire lobe, and in fibroid induration of the lung, the resistance is greater ; but the maximum of resistance is reached in cases of cirrhosis of the lung, with superadded catarrhal pneumonia, and in pleuritic effusion. The resistance is here extreme, and the sensation conveyed to the finger is that of percussing a thick block of wood. It is very important to educate the sense of touch so as readily to appreciate the several degrees of resistance, as this faculty is a great addition to our resources in the matter of diagnosis.