The diagnostic value of von Pirquet's cutaneous reaction is enor mous, most especially so in children. The positive reaction not only indicates the presence of a progressive tuberculous affection, but also that the positively reacting individuals are allergistic to tuberculosis, i.e., that they must have been infected with tuberculosis at some time or other. In view of the frequency of small tuberculous foci in adults, the positive findings of cutaneous reaction, therefore, reveal in their ew just as little, as say the febrile reaction of a subcutaneous injection. In children, however, matters are different, seeing that there arc but rarely latent tuberculous foci. The younger a child is, the more important is the positive result of Pirquetisation.
The advantages of Pirquet's procedure over the subcutaneous method are the following: Simplicity and rapidity in both inoculation and results, there being no injections or taking temperatures; absolute harmlessness, there being neither fever nor subjective or objective manifestations; only one or at the most two inoculations as compared to the necessity of repeated subcutaneous injections with increasing doses; nor does the presence of fever interfere with Pirquetisation. The disadvantages are very slight, considering the value of the reaction: In miliary tuberculosis, cachexia and near the end of life Pirquet's method \\ill fail, but in these cases the subcutaneous injection is but rarely instituted. Besides, if cachectic individuals should recover, an originally negative reaction may turn to positive, as I had myself occa sion to observe in one case. In measles, shortly before the eruption of the exanthema and until about the ninth day after its disappearance, there is seemingly no more allergy, so that the reaction even in the tuberculous will be to all intents and purposes negative. This is probably also the case in croupous pneumonia.
Again, the reaction may under certain circumstances be negative at first and turn to positive on repeating the inoculation, because the first inoculation has sensitized the subject by the introduction of traces of tuberculin (Pirquet). For this reason I have made it a rule for some time past to repeat the cutaneous inoculation if the reaction should be negative after eight days, and ever since this rule has been followed, the reliability of the reaction leaves nothing to be desired. This, however, alters nothing in the fact that the subcutaneous injection is far superior to cutaneous inoculation.
It may, however, be admitted that a positive reaction may occa sionally be simulated in nontuberculous children. With increasing experience these misinterpretations may be avoided; nevertheless, there are individuals so "reactable*" that the introduction of any heterogeneous substance, which includes tuberculin, causes a slight reaction. Here again repetition of the test is the best means to avoid a pitfall. If the individual is tuberculous, the second reaction will be the more pro nounced; otherwise it will either not occur at all or only to a very slight extent.
A positive reaction will completely disappear in a few days, weeks or months. If, as is sometimes the case, there is much itching at the climax of manifestations or in the healing period, the application of an indiffer ent ointment may be necessary. It may also be possible, as was pointed out before, that in subcutaneous injection the places where previously cutaneous inoculation had been practiced, will again flare up.
Pirquet's cutaneous inoculation should be applied in every case where there is the least suspicion of tuberculosis; it is the method of choice for the general practitioner. It is also well adapted to the require ments of wholesale examinations in schools, orphanages, etc.
Soon after Pirquet's reaction became known, numerous modifica tions and other forms of the allergy test were proposed, but the one inaugurated by Moro-Doganoff in which tuberculin is pereutaneously applied, is the only one of practical importance. Moro terms the same "salve reaction" and employs the following ointment: R . Tuberculin. Kochi 5 c.c.
Lanolin. anhydric 5. 0 M. fiat unguent.
Seeing that 5 c.c. of tuberculin weigh 6 grams, this tuberculin oint ment would contain about GO per cent. of tuberculin in weight. A little of the salve, the size of a pea, is, according to Moro's instructions, rubbed with the finger into the skin (back, chest or abdomen) for about a minute; in my own opinion a glass rod, thickened to a knob at the end, would be preferable for this purpose. The diameter of the treated part of the body should not exceed o cm. and the place be kept exposed for ten minutes. A protective bandage is not required. The typical reaction consists in t he appearance of more or less numerous, red, nodulous efflor escences at the place of inunction, somewhat resembling tuberculids.