It will be perceived that the majority of these symptoms would not be recognized in the lower animals, and the few that would be apparent, such as unsteadiness of movement, attacks of vertigo (megrims), or twitching in the extremities, would possibly not be attributed to disease of the heart, and would probably not be in any way connected with disturbance of that organ. Under such conditions it is evident that a diagnosis must necessarily be of an uncertain character, unless by some accident suspicion of the true cause be aroused, and a careful examination of the heart lead to the detection of certain morbid conditions.

Physical Examination Of the Heart and its larger vessels can only be undertaken by an expert who is familiar with the anatomy and physiology of the organs of the circulatory system, and on this part of the subject the reader is advised to consult the sections on the anatomy and physiology of the heart. Armed with the knowledge thus obtained, even the tyro will be able to realize the importance of constant experience in the use of the instruments which are employed for the purpose of the examination of the heart and vessels, even if he does not contemplate devoting himself sufficiently to the subject to obtain the necessary skill. In the first place, the examination which will be required will have regard to what can be ascertained by the use of the hand applied to the cardiac region, and also to certain of the most superficial arteries. The amount of force exercised by the heart in its contraction produces a distinct impression to the hand of the examiner when placed upon that part of the walls of the chest against which it strikes or beats, and the impulse communicated by the heart to the blood which passes through the arteries produces a beat as nearly as possible at the same time as the contraction of the heart. This is described as the pulse, and upon its character and frequency some opinion may be formed as to the general condition of the central circulatory organ, as previously described in the section relating to the symptoms of disease.

In the next place, percussion over the cardiac region, performed by a light but sharp stroke with the points of the fingers, will make the examiner acquainted with any alteration in sound as compared with that emitted from the chest of the perfectly healthy subject. For example, where dulness of sound is found to extend beyond the area of the healthy heart, enlargement or hypertrophy of the organ would be suspected.

Next to percussion, auscultation is employed by the use of the stethoscope in human practice, by the application of the ear to the part where the lower animals are concerned.

The object of this form of examination is to distinguish any abnormal sounds which may exist in connection with the beats of the heart. These sounds can only be distinguished by the expert who is familiar with the healthy sounds, which may be described as far as it is possible to describe them in words as follows: - First, there is a sound which is believed to be produced by contraction of the ventricles. This is called the systolic sound, and it is also distinguished as a long sound, the term being used, of course, comparatively. This systolic sound is followed by a short interval of silence, which is succeeded by the second, described as the diastolic sound, which occurs when the ventricles cease to contract, and the valves guarding the pulmonary vessels and the aorta close. The diastolic sound is followed by a rather longer silence than that which succeeds the first, and then the systolic or first sound recurs. The duration of the sounds and intervals is expressed by dividing the whole period occupied by the series into ten parts, and then subdividing as follows: - Systolic sound 4/10, first interval 1/10, diastolic sound 2/10, and second interval 3/10. The actual character of the sounds as they strike the ear has been expressed by Dr. C. J. B. Williams by the words "lub-dup". Very little difficulty would be experienced in rendering the ear accustomed to the normal sounds of the heart, but it must be clear that an acquaintance with the abnormal sounds and their meaning could only be acquired by long practice with the assistance of a competent instructor. The most that the tyro could hope to achieve in this direction without such assistance would be the recognition of a change from the normal sound of the heart or its large vessels, and he would arrive at the knowledge simply from the observation that the normal sound with which he had rendered himself familiar had undergone certain modifications.

The expert, in making an examination, not only realizes the fact that there is a change from the normal sounds to the abnormal, but he distinguishes also the seat and cause of the abnormal murmurs; for example, variations as to the intensity of sounds, whether increased or diminished, alteration with regard to pitch and clearness of the systolic sounds, will inform him as to the condition of the valves and walls of the heart. A very clear, sharp, high-pitched, systolic sound will be more commonly heard in cases of anaemia, or extreme debility; again, alterations in the duration of the sound give important information as to the condition of the heart. In dilatation of the ventricles, with increase in the thickness of the walls, the systolic sounds will be prolonged, and the diastolic sound will probably be much shortened and very much obscured; whereas, in dilatation of the cavity, without any alteration in the thickness of the walls, the diastolic sound is longer than normal, while the systolic is shortened.

The pathologist also obtains a great deal of information while examining his patient by comparing the sounds which are heard in different parts of the chest, especially over those parts which correspond to the lower part or apex and the upper part or base of the heart. If the sounds are weak at the apex and louder at the base, the evidence is accepted as serving to distinguish effusion into the heart-sac (pericardium) from dilatation of the cavities or fatty condition of the heart. Intense sound at the right apex over and above that at the left may indicate either displacement or enlargement of the right side of the heart; it also occurs when a portion of lung unduly distended with air (emphysematous) is interposed between the heart and the walls of the chest.

A murmur or, as it is commonly called, " bruit" is generally taken to indicate friction at some point over which the blood is passing, and in the majority of cases it is allowed that the murmur depends on some morbid condition of the valves which guard the orifices of the heart.

There are certain situations in which the murmurs relating to different parts of the heart are most readily heard. Thus murmurs connected with the mitral valves (fig. 191) are described as loudest just above the apex beat, while the murmurs which are connected with the valves of the aorta are most marked at the base of the heart. In the descriptions which are given in works on pathology a much more intricate and extended account of the different sounds in different positions is given, but sufficient has been written to indicate to the reader the very abstract character of the subject, and the enormous difficulties which attend a critical examination of the heart with a view of making a correct diagnosis of any existing disease. Indeed, with all the facilities which the physician possesses, including the use of the most elaborate and perfect instruments, the power to place his patient in any position which he thinks most convenient, and of regulating the character of the respirations with regard to their depth and frequency, or of arresting the action altogether for a short period, so as to obtain absolute silence in the respiratory organs of the chest, there is still a considerable difference of opinion existing among experts as to the cause and meaning of certain sounds which can be recognized.

Diseases of the heart and its connections are for convenience divided into those which affect the membranes enclosing and lining the organ, and those attacking the muscular structure of which it is chiefly composed. Thus we have acute or chronic inflammation of the membranous sac in the double layer of which the heart is completely invested, and similar affections involving the fine membrane which lines the cavities of the heart, and these two morbid states are designated by different terms according with the position occupied by the structures. Where inflammation affects the former it is spoken of as 'pericarditis, or inflammation of the investing membrane; while the term endocarditis is used to indicate inflammation of the membrane which lines the cavities of the heart and contributes to the formation of the different valves. Inflammation of the valvular structures is also distinguished by the term valvulitis. Inflammation, acute or chronic, of the muscular structure of the heart is described as myocarditis, which is commonly associated with inflammation of the membrane investing or lining the heart.