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avirulent, but they must be living. The work of Calmette and G-eurin supports this, and their extensive experimental work in connection with the non-virulent strain of bovine bacilli, named by them 8.C.G., is an interesting and promising attempt to confer immunity on new-born babies. Their results are at present being discussed, and their claims are receiving criticism at the present moment. The effect of inoculation with tuberculin in a non-tuberculous animal is to induce a state of sensitiveness to the tubercle bacillus and its products, but there is no evidence to show that this sentiveness implies any degree t>f immunity. In the words of Kolmer, " Few subjects in medicine are as perplexing as the nature and mechanism of the action of the tuberculins, despite a very large amount of clinical and laboratory investigation. Brought forward by its great discoverer as an immunizing and therapeutic agent, we have since learned that its immunizing-power is almost negligible, and its application in treatment surrounded by definite limitations." To sum up, definite immunity to tuberculosis in the non-tuberculous subject is only obtained by infection with living tubercle bacilli; there is no satisfactory eivdence to show that either in man or in experimental animals this result can be obtained by tuberculin. (2) The Value of Tuberculin as a Therapeutic Agent in Pulmonary Phthisis. Tuberculosis is unlike most other infectious diseases, in that it tends to produce a number of circumscribed local lesions surrounded with fibrous tissue ; the centre is usually necrotic, and the blood-supply tends to be obliterated by endarteritis. Now, the production of immunity depends probably on two main factors—(l) The elaboration of antibodies which are carried in the blood-stream ; the site and method of elaboration we do not know : (2) immunity produced locally by the tissue at the site of the lesion, in the form of immune bodies, which are also carried by the blood-stream to all parts of the body. Now, the centre of the caseous tuberculous lesion has no blood-supply, and it is difficult to see how any effective lethal power can be exerted in the midst of this mass by means of substances carried in the blood-stream. The periphery of the lesion is composed of more or less avascular fibrous and granulation tissue. Consequently, penetration seems improbable. Local immunity at the site of the lesion may be increased ; or, at any rate, the fibrous barrier may be stimulated to proliferate, and thus wall-off the diseased area. It is probable that, if tuberculin has any salutary effect, it is in this latter way. It has been found, however, that a dose sufficient to excite a constitutional reaction usually causes a breaking-down of this fibrous barrier and the spread of the disease. In any case, there is an increased local congestion (focal reaction), which carries off poisonous products and very probably tubercle bacilli. Consequently, very small doses are the rule, with a gradual increase till, after a long period, large doses can be tolerated : but in no case is a definite general reaction allowed. A local reaction (at the site of inoculation) may be obtained, and the assumption is made—which I consider unproved —that a focal reaction also occurs (at the site of the lesion). It is generally accepted that in vaccine therapy generally (and tuberculin treatment belongs to this category) immunological response is only obtained when the dose is sufficient to excite a focal or general reaction. In this case a general reaction is avoided and a focal reaction presumed. The tolerance to doses of tuberculin does not prove that immunity to tuberculosis has been established. That some patients improve after or during tuberculin treatment is certain : that this improvement is due to the tuberculin is open to grave doubt. It is not improbable that the doses exhibited have little or no effect other than a psychological one. It is quite clear that tuberculin may be dangerous, and that it is harmful to some patients under certain conditions. Landis, writing in the " Oxford System of Medicine," says that the best that can be said of it is that in the vast majority of cases it exerts no influence whatever. While treatment of certain forms of surgical tuberculosis with tuberculin may find stronger advocacy, it seems to me that the use of tuberculin in pulmonary phthisis presents special dangers owing to the vascularity and looseness of the pulmonary tissues. The fact that after thirty years' trial no general agreement has been reached as to the value of tuberculin, and that amongst its advocates no two agree as to form, dosage, or interval between doses, may reasonably induce a scepticism as to its therapeutic value, particularly in pulmonary phthisis. Its use in surgical tuberculosis may be partly due to the fact that it is less dangerous in these cases. Tuberculin must be regarded as one of the most disappointing of the specific therapeutic agents introduced by bacteriology. R. E. Be van Brown,

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