If this method cannot be employed, as for example in tuberculosis of the liver, brain, etc., and the diagnosis is uncertain, the use of tuberculin constitutes the surest and easiest method of coming to a conclusion. Nocard’s researches have shown the precautions to be observed. A minimum febrile reaction of 2° Fahr. (1·5° C.) is, however, necessary before the existence of the disease can be affirmed.
Lastly, there remains a less rapid method, which aims at transmitting the disease to specially susceptible animals by inoculating with suspected materials, such as the nasal discharge, pus, milk or pulp of internal organs. This method is most valuable when bacteriological examination has failed and tuberculin has produced only doubtful results. The guinea-pig is the subject usually chosen, but some weeks, or even months, may elapse before definite results are obtained.
In those forms where ordinary methods of investigation prove sufficient it is well to bear in mind the symptoms which differentiate this disease from others closely resembling it.
Pulmonary tuberculosis, for example, should always be suspected whenever there exists frequent coughing, nasal discharge and poor bodily condition; if in addition to this respiration is found on auscultation to be rough, inspiration interrupted or rasping, expiration prolonged or blowing and the vesicular murmur non-existent, suspicion becomes almost a certainty. The diagnosis is even more assured if the respiration is of a blowing character at certain points, accompanied by snoring and sibilant râles and gurgling or cavernous souffles.
The distinction between pulmonary tuberculosis and chronic bronchitis or simple pulmonary emphysema is based on the increased resonance revealed by percussion in the latter case; the different character of expiration; the existence of a double breathing movement; the external appearance of the animal; the absence of bacilli from the nasal discharge, and the failure to react to tuberculin.
The condition cannot be mistaken for verminous broncho-pneumonia if the information furnished by auscultation and the results of microscopical examination of the discharge are taken into account, the eggs or embryos of strongyles being extremely easy to detect.
Tuberculosis of the pleura may be mistaken for peripneumonia if the observer trusts to percussion alone, but the auscultation sounds are then different, and an injection of tuberculin will remove any doubt.
Tuberculosis of the peritoneum is often suggested by the indications afforded by careful palpation (thickening of the walls of the abdomen, rigidity and sensitiveness), and is distinguished from ordinary acute peritonitis by the difference in the appearance of the animals and the absence of much fluid. Chronic exudative peritonitis and ascites also exhibit sufficiently well-marked characteristics to enable them to be differentiated from tuberculosis of the peritoneum, but this is certainly not true of adhesive peritonitis, and in cases of the latter kind tuberculin is the only means of confirming the diagnosis.
External tuberculosis of the retro-pharyngeal and cervical lymphatic glands resembles, at a first glance, simple inflammation of lymphatic glands, but in the last-mentioned disease the lesions are symmetrical and the glands still retain a certain amount of elasticity, whilst in tuberculosis they are bosselated, hard, and sometimes fluctuating.
Tuberculosis of the mediastinum is suggested by difficulty in swallowing, especially if tympanites follows soon after eating, eructation is absent, and rumination is arrested.