The conclusions to be deduced from this brief series of experiments are as follows:
1. The ophthalmo-tuberculin reaction is of some value for diagnosis of tuberculosis in cattle. A characteristic conjunctivitis with fibrinous exudation coming on from six to eight hours, reaching a maximum in from sixteen to twenty-four hours and disappearing in forty-eight hours, is noted in tubercular animals.
2. The reaction is more pronounced in those animals which have not been recently tested with tuberculin. With this reaction as with the usual tuberculin test one injection and reaction probably inhibit a second reaction during a period from six weeks to a year. The ordinary tuberculin test does not seem to interfere to any great extent with the ophthalmo-tuberculin test at least within four weeks. Class B, though recently tested, showed the reaction, although not to the extent of Class A, which was tested some time ago. The tuberculin test occasionally prevents absolutely a second reaction, and usually no second reaction occurs within six weeks to a year, as before stated.
3. In cattle recently tested with tuberculin by the subcutaneous method the ophthalmo-tuberculin reaction is only slightly reduced in its intensity. The ophthalmic test may possibly serve as a means of diagnosis of tuberculosis in cattle which have been tested with tuberculin by the ordinary method and will not react a second time, or where tuberculin has been injected into cattle in order that they may clear a second test.
Another possibility must not be overlooked in this connection. It is well known that animals which have a slight tubercular infection often show a very marked and typical reaction to the tuberculin test as it is usually made, and those animals which show themselves clinically to be in the advanced stages of tuberculosis often show only a very slight reaction. The animals in Class B are in the advanced stages of tuberculosis and this fact might perhaps account for the lower intensity of the reaction. The exact cause of the lower reaction in these cattle can only be determined by further experimentation.
4. No constitutional disturbance being noticed in any of the cattle tested, that is, no rise in temperature, loss of appetite or falling off in the production of milk, it is evident that the instillation of tuberculin into the eye does not produce the general reaction which attends in some cases the subcutaneous injection of tuberculin, and is therefore decidedly advantageous. The exudate disappears and leaves the eye perfectly normal in forty-eight hours after injection.
5. If the ophthalmo-tuberculin test proves as efficacious as the foregoing experiments seem to indicate we have in it a comparatively rapid and easy means of diagnosing tuberculosis in cattle. Such being the case the method cannot fail to come into general use superseding the present laborious method of applying the test. Cattle can be injected and then inspected sixteen to twenty-four hours afterward.
There are many problems in connection with the reaction which must necessarily be studied. The following are a few of the propositions:
1. Is it possible to tell by the reaction how far the tubercular process has progressed in the body?
2. Is there any relationship between the intensity of the reaction and the number and severity of the tubercular lesions?
3. Will the test prove to be more accurate than the ordinary tuberculin test which is said to reveal all but four per cent. of the cases ?
4. Will the test reveal tuberculosis after a subcutaneous tuberculin injection?
5. Will animals react a second time if the first tuberculin is placed in the eye and the second given by the ordinary subcutaneous method and conversely?
These and many more points must be thoroughly investigated before the efficiency of the test is proven.
The opththalmo-tuberculin test will be repeated on other cattle, and also on the cattle used in these experiments. Experiments are being made to determine the efficiency of the cutaneous tuberculin reaction in cattle. We wish in this paper to give only the preliminary findings.