It seems to be agreed among veterinary writers that diseases affecting the heart of the horse are either not so numerous as those which attack the heart of the human subject, or that they pass to a great extent unnoticed until an opportunity is afforded for a post-mortem examination.
Going back to the work of Gibson, who wrote in 1751, it will be observed that after a description in detail of the structure and functions of the heart and large vessels, he dismisses the pathology of the organ in a short paragraph. " I have seen", he says, "the hearts of horses frequently opened; sometimes there happens, as in the human body, collections of matter within the pericardium. I have seen pollipusses in the great vessels, sometimes a mass of slippery fat, especially within the left ventricle of horses that have died suddenly, and sometimes the heart itself is preter-naturally large."
Since the time of Mr. William Gibson, surgeon, knowledge has advanced, but even at the present day the subject of disease of the heart and large vessels is dealt with by veterinary writers in a very cursory manner.
In the last edition of Mayhew's work on the horse, edited by Mr. James Irvine Lupton, it is remarked that disease of the heart is characterized by various names in scientific books, as carditis, pericarditis, hydrops-pericardii, inflammation of the pericardium, etc. All such conditions, the writer observes, in the horse were discovered by examination instituted after death, when, unfortunately, all opportunity of observing symptoms had ceased. Veterinary science cannot distinguish one state from another while life exists. May hew goes on to state that "diseases of the heart in horses are incurable", and suggests that it is possibly on that account that "apparently little attention has been paid to the diagnosis and treatment of them". Remarking on the absence of characteristic symptoms, he adds that auscultation affords the surest means of detection. Any unusual sound, he says, being audible, the examiner may conclude that the heart is diseased. In further description of symptoms it is stated that " the visible signs are sometimes sufficiently emphatic to admit of no doubt"; the eye is expressive of constant anguish, the countenance is haggard, the pulse is feeble and irregular, and the heart-throbs are visible and frequent; they are to be seen as plainly on the right side as on the left. Regurgitation within the jugular; veins is nearly always excessive, the blood often reaching almost to the jaw."
The difference between the estimated importance of heart-disease in man and the lower animals is emphasized by Mayhew, and indeed is urged in explanation of the comparative indifference with which these diseases have been regarded by the veterinary surgeon. The veterinarian is seldom called upon to treat heart-disease, and has not the same experience of diseases affecting this organ as has the physician, for the reason that man, even when suffering from an incurable ailment, must be treated, but the horse in a similar state is usually sent to the knacker; consequently it is from human medicine that the most valuable information has been received. These remarks are strictly correct, and fairly estimate the circumstances which have enabled the members of the veterinary profession to recognize the clinical symptoms of some of the diseases of the heart of the lower animals, which they can now diagnose with almost absolute certainty, although it still remains true that the physician has enormous opportunities and facilities in the examination of the heart of the human subject which are not, and cannot, under any possible conditions, be possessed by the veterinary surgeon. The heart of the horse and other large mammalians is so perfectly covered by the bones and muscles of the upper part of the fore extremities that it is absolutely impossible to apply the stethoscope or the ear over every portion of the organ, as can be easily done in the human subject; further, the instrument cannot be employed with the same advantage as it possesses in the hands of the physician. Even in those parts which can be reached, the covering of hair interposes an obstruction which considerably alters and obscures the sounds which can be recognized, and it is on this account that the majority of veterinary surgeons content themselves with the application of the ear to the part of the animal which they wish to auscultate instead of using the stethoscope for the purpose. In this connection, however, it may be observed that the ear is a very poor substitute for the stethoscope wdien the latter is in a practised hand aided by an educated ear.
Of the fact that the heart in the lower animals is subject to most of the diseases which are well known in the human subject, the experience which has been gained by post-mortem examination has afforded abundant evidence, and the veterinary pathologist has no difficulty whatever in recognizing the true characteristics of the various morbid conditions which are exhibited after death. His difficulty is confined entirely to the detection of each special form of disease in the living animal, and while he would not be content to accept Mayhew's imputation, that veterinary science cannot detect one state from another while the animal is alive, he would without hesitation admit the great difficulty of arriving at a satisfactory conclusion from symptoms which may be present at the time of his examination. Certainly it is the case that some of the most marked symptoms which Mayhew describes would not necessarily suggest to him the existence of any disease of the heart.
In connection with the subject of clinical symptoms it is fully recognized by the physician that the evidences of disease, or evidences which may be construed into signs of disease, of the heart, may be present in parts of the system remote from the organ itself. There is nothing at all remarkable in this proposition when it is remembered that the heart is the organ which distributes the blood over the whole of the body, and is therefore connected more or less directly with every other part of the system.