SECTION IV.. The Organs of Circulation.

THE ORGANS OF CIRCULATION.

SEMIOLOGY OF THE ORGANS OF CIRCULATION.

The semiology of the circulatory apparatus comprises the clinical examination of the heart, arteries and veins, and the examination of the pulse and blood.

=Heart.= In animals of the bovine species, the heart is situated in the thoracic cavity opposite the third, fourth, fifth and sixth ribs, nearly in the median plane of the thorax, and inclined from front to back at an angle of 70 degrees.

The pericardial sac touches the extremity of the sternum where it is in immediate contact with the lower insertion of the diaphragm. This peculiar arrangement favours the development of pericarditis due to foreign bodies.

On the left side the pericardial sac may come in direct contact with the internal surface of the thoracic cavity opposite the lower extremity of the third, fourth, and sometimes fifth ribs. At all other points the pulmonary lobes, as expanded during inspiration, separate it from the thoracic wall.

Although the pericardium and heart are situated in the median plane, percussion and auscultation should be performed on the left side, since the anterior and cardiac lobes of the left lung are less developed than those of the right; but the heart can be auscultated on the right side, as is advisable at times.

In the healthy ox there exists an area of the left thoracic wall which may be called the cardiac zone, on a level with which are heard the normal heart sounds. In diseased conditions this zone or area may vary in size, and the sounds may be modified.

The heart can be examined by inspection, palpation, percussion, and auscultation.

Under ordinary conditions inspection reveals nothing in well-nourished animals; but in very thin subjects and in those suffering from recent cardiac lesions or pseudo-pericarditis, a rhythmic movement of the chest wall is sometimes detected.

Palpation is performed by placing the open hand on the cardiac zone. In this way the cardiac shock can be felt, its degree of intensity judged, and, in an imperfect manner, its rhythm.

Percussion by means of the fingers or a pleximeter discloses the extent of the physiological area of partial dulness, due to the presence of the heart, as well as its variations in pathological conditions, particularly in pericarditis with marked exudation.

In such cases there may even be complete dulness when the distended pericardium thrusts upwards the corresponding pulmonary lobe, and comes in contact with the internal surface of the thoracic wall, or, in cases of pericardial pneumatosis, exaggerated resonance, and a tympanitic sound.

Auscultation is carried out either directly or by the stethoscope or the phonendoscope. The normal or pathological sounds of the heart are thus ascertained, as well as the intensity of the cardiac beats and sounds, the frequency of the rhythm, etc.

When injuries have occurred which cause murmurs, it is best to use the stethoscope and to apply it at the points where murmurs are heard at their maximum intensity, i.e., exactly at the spot where the cardiac shock is noted, and towards the base, in the region where the great arterial trunks begin.

In the latter case it is often useful to draw the left fore leg forward.

=Arteries.= The arteries are rarely the seat of lesions that can be detected by examination, and therefore such examination is usually limited to noting the state of the pulse.

Arteritis and thrombosis of arteries are rare, and although lesions of atheroma have been discovered in certain chronic diseases, such as tuberculosis, chronic diarrhœa, etc., they are difficult to detect, even on examination per rectum of the bifurcation of the aorta.

=Pulse.= The examination of the pulse, on the contrary, is of great importance. In animals of the bovine species the pulse may be taken at a number of different points, such as the submaxillary artery, on the side of the lower jaw: in the case of very thin animals at the radial within and in front of the elbow joint; at the internal saphenous artery, at the height of the mamma or scrotum; or at the coccygeal artery, at the base of the tail.

This examination reveals the frequency (50 to 60 per minute), the quality, whether strong, feeble, imperceptible, etc., the regularity, etc., etc.

=Veins.= The veins are more easily examined than the arteries, on account of their superficial position in most cases.

Inspection and palpation are the only means of examination.

Inspection shows the degree of fulness or collapse, and also the existence or absence of what has been termed venous pulse.

Venous pulse occurs only at the lower extremity of the jugulars. It is very frequent in animals of the bovine species, and in thin animals is not necessarily a pathological symptom. It is due to reflux of blood in the anterior vena cava, under the influence of the expiratory effort; sometimes to emphysema, tuberculosis, etc.; in other cases to the return of blood towards the vena cava and jugulars at the moment of auricular systole, as a result of lesions of the tricuspid or auriculo-ventricular orifices.

By palpation of the veins their permeability can be estimated, also the degree of distension or obstruction, and the condition of their contents.

=Capillary system.= Among methods of arriving at the state of the circulatory system must be included an examination of the vascular condition of the accessible mucous membranes, such as those of the eye, mouth, nostril, vulva, etc. This examination is easy to carry out, and is of value in diagnosing congestive states, pneumonia, and local inflammation.

=Blood.= Examination of the blood is sometimes necessary for the exact diagnosis of certain diseases, and therefore should be carried out whenever occasion requires. The physical state, coloration, and rapidity of coagulation afford valuable data in certain diseased conditions, and indicate the approximate richness in hæmoglobin, the normal or abnormal composition of the plasma, and the richness of the blood in white corpuscles.

Microscopic examination is still more valuable, whether carried out by the moist method, in which a drop of blood is compressed under a cover glass, or the dry method with or without staining. In the latter case the specimen is fixed with a mixture of equal parts of alcohol and ether or by immersing it in a 1 per cent. solution of osmic acid.

By this means it is possible to detect the condition of the red and white blood corpuscles and hæmatoblasts; the existence or non-existence of leucocytosis and its degree, as well as the existence, for instance, of leucocythæmia.

The blood corpuscles may also be counted.

Histological examination, supplemented by suitable staining, reveals the presence of normal or abnormal blood corpuscles, parasites such as piroplasma, or microbes such as bacteria.

Such examination necessarily presupposes a knowledge of what should be looked for in the normal state.

In normal blood the red blood corpuscles predominate. They are all similar in form and, with few exceptions, of the same size. They stain strongly with acid solutions such as eosine. In pathological conditions, large or giant corpuscles may be found (macrocytes), as well as those of medium size (normal) and small size (microcytes). Some are vigorous and stain deeply; others, on the contrary, are degenerating or dead, and have no greater affinity for one constituent than for another of the double or triple stains commonly employed.

In pathological conditions the hæmatoblasts occur in very varying numbers.

The white blood corpuscles found in health may be classified as follows:—

Large and small lymphocytes, each of which has a round voluminous nucleus and a narrow border, and contains a non-granular protoplasm; their proportion varies between 22 per cent. and 25 per cent.:

Polynuclear leucocytes or polymorphous leucocytes with a single nucleus, which originate in bone marrow, stain best with neutral colours, and are present in the proportion of 70 per cent. to 72 per cent.:

Mononuclear leucocytes with an ovoid eccentric nucleus stain best with basic colours, and form about 1 per cent.:

Polynuclear leucocytes stain best with eosine or acid colours, and form about 1 per cent. to 2 per cent.

When these white blood corpuscles are in larger number the condition is known as leucocytosis, and when one or other variety is in very great excess the condition is known as leucæmia.