It would be impossible from these peculiarities alone to identify the nature of the disease which causes such progressive organic wasting, as the continued presence of fever prevents the use of tuberculin, but fortunately the preliminary changes in the lungs, lymphatic glands, genital tract, etc., are sufficient in most cases for the purposes of diagnosis.
Sheep, Goats, and Pigs.—In the other domestic animals tuberculosis is only of secondary importance to the practitioner.
It has been seen in the sheep and goat, but almost exclusively as the result of experiment. It must be understood, however, that prolonged cohabitation with diseased oxen or lengthened sojourn in contaminated places may easily produce tuberculosis in the goat, though the sheep continues to resist for a somewhat longer period.
Clinically such tuberculosis presents little interest on account of its rarity.
The same remark applies to pigs; nevertheless, an entire herd may become infected, and it may be necessary, after making a preliminary post-mortem, to examine the other patients. All forms of the disease occur in pigs, the lung being most frequently affected, but tuberculosis also attacks the intestine, udder, lymphatic glands, joints, etc. The pig, in fact, is extremely susceptible to this disease, whilst the sheep is only subject to it in a comparatively trifling degree.
Diagnosis. The clinical manifestations of tuberculosis are so numerous and so various that it is often an extremely hard task to form a diagnosis. Without doubt detection is relatively easy in well-marked forms, such as tuberculosis of the lungs, lymphatic glands and genital apparatus, but even in such cases the symptoms must be reasonably well-marked.
At first, unless the lesions produce externally visible signs, diagnosis is impossible, and in the case of hidden forms, such as tuberculosis of the serous membranes, mediastinum, intestine, testicle, etc., all that can be done is to take into account the probabilities.
Clinical diagnosis is therefore possible, but only in exceptional cases can it be absolutely relied upon. Fortunately, methods of investigation increase and become more exact every day, so that the points which clinical examination is incapable of deciding are often cleared up in the laboratory. Bacteriological examination of morbid products, such as the nasal discharge, the products of suppuration, the milk or the diseased tissues, is a valuable means in many cases of determining the presence of the organism which causes the disturbance. In all cases, in fact, the tubercle bacillus should be sought for in order to confirm the diagnosis.
Fig. 283.—Tuberculosis of the posterior mediastinal lymphatic glands in a sheep which had been kept for two years in company with some tuberculous cows. PG, Left lung; PD, right lung; T, trachea; La, anterior lobes; L, middle cardiac lobes; Lp, posterior lobes; Gm, tuberculous and enlarged posterior mediastinal lymphatic glands.