334 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



The high percentage of positive findings in non-suspected cases 

 is readily explained, if we bear in mind how common a latent, 

 inactive tuberculosis actually is. 



As to indications and contra-indications it will suffice to state that 

 the test may be made in all suspected cases unless heart lesions, 

 diabetes, nephritis, or pregnancy exist, or unless laryngeal tuber- 

 culosis is suspected. 



To illustrate the general safety of the procedure, providing that 

 the rules of dosage given above are implicitly followed, we would 

 point out that Lowenstein did not meet with any serious symptoms 

 or a single death in a series of 20,000 single injections which were 

 made under his direction. 



The Tuberculin Test According to v. Pirquet (Cutaneous Method). 

 The inner surface of the forearm is cleansed with ether, then two 

 drops of the concentrated old tuberculin of Koch are placed about 

 10 cm. apart. With a special instrument, which v. Pirquet terms 

 an "Impfbohrer" (vaccination gimlet), and which is essentially 

 an exceedingly fine chisel with a platinum-iridum point that can 

 be sterilized in a flame, a small abrasion is first produced midway 

 between the two drops. To this end the instrument is pressed 

 against the skin and rotated, sufficient force being employed to 

 produce a definite abrasion, without, however, causing any bleeding. 

 A similar scarification is then made through each one of the two 

 drops of tuberculin. A tiny bit of sterile absorbent cotton is now 

 laid across each drop so as to prevent it from flowing away. After 

 five minutes this is removed. A dressing is not used. Should 

 examination at the expiration of twenty-four to forty-eight hours 

 not reveal the existence of a distinct brown scab measuring about 

 1 mm. in diameter, both at the point of inoculation as well as at that 

 of control, the abrasion has been too slight, and the test must be 

 repeated. 



The appearance of a positive reaction when fully developed is 

 well shown in Plate VIII, and contrasts markedly with that of the 

 control. If the abrasions are examined at frequent intervals it will 

 be observed that a small wheal appears within a few minutes both 

 at the control and the test-point which soon becomes surrounded 

 by a pink halo. This disappears after a few hours, leaving a small 

 red area, in the centre of which a tiny scab begins to form. At 

 the control-point the redness is still discernible after twenty-four 



