Local reactions have been described years ago by Epstein, Esche rich and Schick, but in those early publications the difference between puncture and subcutaneous reactions has not been sufficiently empha sized and what is now known as "Depot" or subcutaneous reaction was included in the designation of puncture reaction. Latterly great value has been attached to the subcutaneous reaction by Hamburger as a decisive sign for the presence of tuberculosis.
The subcutaneous application of tuberculin for the purpose of establishing the diagnosis of tuberculosis is still to-day the subtlest and safest method. It is not applicable in febrile cases; it requires taking the temperature every two hours; rest in bed; nearly always clinical obser vation, and devolves a certain measure of inconvenience upon patient and attendant alike. Toward the end of life it may fail in individual cases. But these disadvantages are outweighed by the absolutely safe findings with correct procedure.
However, the tuberculin test had not met with general appreciation for diagnostic purposes until von Pirquet introduced, in 1907, its cutane ous application. This author explained the reaction in tuberculosis by assuming that the tuberculous individual is allergistic to tuberculin, which means that his reactive capacity is different from that of the healthy, or rather nontubereulous individual. This, for instance, is also exemplified by the fact that cutaneous inoculation of tuberculous subjects with tuberculin produces a focus of inflammation in the shape of a papule, measuring from 5 to 20 min. in diameter. In his first experi ments von Pirquet availed himself of a 25 per cent. tuberculin solution, but later he has decided to use undiluted tuberculin in all cases.
The technique in producing a cutaneous reaction (Pirquetisation) is as follows: The part of the body where the reaction is intended to take place (upper arm, lower arm, lower part of the thorax) is cleansed. One droplet each of undiluted tuberculin is applied to two spots of the skin about 6 to 10 cm. apart. By means of a serviceable instrument, such as Pirquet's original instrument, an inoculating lancet, needle or something similar, the skin midway between the two droplets, or just above, is so lightly scratched that not a particle of blood may exude. This is done as a control. Next, with the same instrument, t he same degree of energy, and in exactly the same way, the two places are lated, on which the two droplets of tuberculin had been deposited. The
excess tuberculin is neatly removed with a cotton swab, care being taken that no part of the tuberculin may come in contact with the trol scratch. This completes the inoculation. No bandage is sary, but no harm is done by ing a cotton layer which should be fixed with adhesive plaster. It is advisable to use the set of instru ments introduced by von Pirquet for two reasons: (1) By using the iden tical instrument in all eases, the reactions obtained will admit of com parison in regard to intensity, and (2) the skin may be easily scratched too deeply when a strange instrument is used. Pirquet's instru ment a very slight drilling motion is executed. Any hremorrhage de stroys the test.
One hour later all the three lesions of the epidermis will show uni form slight hyperremia, but while this will disappear after a few hours at the control scratch, there \VIII appear a round hypertpinic elevation and infiltration around the two inoculated scratches, if the individual is tuberculous. The diameter of these specific infiltrates varies between 3 and 50 mm. and may occasionally lead to a somewhat more extended hyperremia in the vicinity of the actual inoculated area. In the majority of cases the reaction will be distinctly visible in twenty-four hours, when in some cases it has already its climax. The best opinion can be formed of the reaction after forty-eight hours, and for this reason I always have the inoculated children brought to me after the lapse of that time. I should not omit to mention, however, that there are cases in which a decision as to the positive nature of the reaction cannot be arrived at until three, four or more days have elapsed.
The appearance of the reaction varies with the length of time that was required for its occurrence. In some cases it may be bright red, very prominent and considerably raised above the level of the skin, with a central indentation showing the actual spot of inoculation; in other cases it is almost bullous; in others again it is hardly raised at all, dull brown in color, and hardly showing any traces of a true inflammation, so that the reaction gives rise to the widest variations. It is the control incision that but rarely leaves a doubt as to whether the reaction is posi tive or negative.