Reference has already been made to the sphygmograph, which is used for the purpose of obtaining a tracing of the pulse. This instrument has not come into use in general practice, nor is it probable that it will for some time at least replace the ordinary method of taking the pulse; nevertheless, it may be interesting to examine the above illustrations, which show very clearly how the different tracings are interpreted; and further information on the subject will be found in the treatises on the sphygmograph by Dudgeon, Steell, and others.
Fig. 494. - Sphygmograph Diagrams of the Pulse (after Sanderson, Dudgeon, and Steell).
In the Human Subject. - 1, Normal healthy pulse: a, systolic wave produced by contraction of left ventricle; b, apex of upstroke indicating highest pressure; c, downstroke; d, first tidal or predicrotic wave; e, aortic notch, probably indicating the end of the systolic and commencement of the diastolic action of the heart; f, dicrotic wave due to sudden closure of aortic valves; g, second tidal wave; g to h, period of rest (after Dudgeon). 2, Feeble pulse of age (weak contractility of artery). 3, Senile pulse (muscle failure of heart). 4, Hard wiry pulse of rheumatic fever. 5, Hard and long pulse of hypertrophy of left ventricle with dilatation. 6, Soft pulse of irritative fever. 7, Nervous excitement. 8, Mitral and aortic disease.
11, Haematograph. Blood spurted from a human artery received upon a revolving drum, showing systolic and dicrotic waves (after Landois).
With regard to the respiratory system, symptoms having reference to the number of respiratory movements in a given time, and their character, are almost as varied as are those affecting the circulatory system; thus the breathing may be quick or slow, spasmodic or difficult. Stertorous breathing is attended with a noise which may be compared to snoring. Breathing may also be irregular, sometimes being carried on by the abdominal muscles while the ribs remain fixed, and at other times by the thoracic muscles almost exclusively, as in cases of acute peritonitis. A peculiar form of the expiratory effort is exhibited in the act of coughing, the sound of which is produced by a sudden spasmodic expiration, and varies as to its character in different forms of disease; thus there are described moist, dry, and spasmodic coughs. There is also a cough which is peculiar to the broken-winded horse and to the roarer. A soft painful cough is present in bronchitis of the acute kind, and its character is so well defined that the expert will accept the sound as a diagnostic symptom. A hard, dry, or husky cough indicates the absence of mucus, a fluid which in the normal state moistens the lining membrane of the respiratory tubes, and in one stage of bronchitis, or bronchial catarrh, is secreted in excess and often assumes a purulent character. A dry cough is also a symptom of parasitic bronchitis, which is commonly on this account designated "husk".
Symptoms which are observed in relation to the digestive system are often rather obscure in their indications; diarrhoea, for example, may arise from so many and diverse causes that its presence does not materially assist the examiner in forming a diagnosis. Nervous excitement is capable of inducing it in some horses. The sight of a red coat or other preparations for the hunting-field act on some sensitive hunters much more rapidly than a dose of purgative medicine. Indigestion may be accompanied by this symptom, or the presence of parasites in the intestinal canal may produce the disorder; and it may also be the sign of a critical stage in certain febrile affections.
In the opposite state, i.e. constipation, the same difficulties occur in the endeavour to interpret the symptom, and in both cases it becomes necessary to take cognizance of other symptoms in order to arrive at a correct conclusion.
Diarrhoea or constipation, in association with a yellow tinge of the mucous membrane or the skin, or of both, will naturally lead to a suspicion that derangement of the liver is the primary cause. This symptom is also prognostic, as it points to the necessity of treatment being directed to the liver rather than to the digestive tube.
Disorder of the urinary organs is usually marked by obvious changes in the quantity and character of the urine secretion, and the practitioner frequently gains valuable information by observing that the secretion is excessive, defective, or altered in character. An examination by means of the microscope and the application of chemical tests are among the means which the modern veterinarian employs to complete the evidence on which his diagnosis must be based.
It is not of course expected that the horseman will devote himself to the study of symptoms sufficiently to master the subject thoroughly, but he cannot fail to be interested in an account of the methods which are employed by professional men to arrive at correct conclusions as to the localization and pathological character of the derangements which it is their object to rectify by the use of appropriate remedies.