522 IMMUNOLOGY 



primary tuberculosis. The roentgenologic findings are of great 

 value, however, in the diagnosis of the reinfection or adult type of 

 tuberculosis. 



Effect of Age Upon Diluted Tuberculin. — In regard to the 

 effect of age upon dihited tuberculin Aronson says that Mantoux as 

 early as 1909 noted that its potency decreased on standing and that 

 Okell found that a 1 :1,000 dilution of OT shows a diminution 

 of potency, if kept at room temperature, of 40 per cent within ten 

 weeks, and 60 per cent within one year. Aronson has observed 

 that a 1 :10 dilution of OT, incubated at 37° C, shows a marked 

 loss of potency within seven to ten days and is practically inactive 

 after several months. Undiluted tuberculin or the purified protein 

 derivative incorporated with beta lactose in tablet form is quite 

 stable. 



System of Grading Mantoux Tests. — Aronson (1934) em- 

 ploys an initial skin test dose of 0.00002 mg. of PPD, reads the 

 results forty-eiglit liours later and reinjects all who are negative 

 with 0.005 mg. of PPD. These doses of the purified protein de- 

 rivative correspond to 0.01 mg. and 1.0 rag. of OT, respectively. 



The system of grading which he has finally adopted is a slight 

 modification of the one previously recommended by the National 

 Tuberculosis Association. He says that the new system of grading 

 enlarges the two-plus range and thus takes in some that were 

 formerly graded three-plus. The new classification of tuberculin 

 reactions is as follows: 



+ Some redness and an area of edema more than 5 



and less than 10 mm. in diameter. 

 + + Area of redness and edema 10 to 20 mm. in dia- 



meter. 

 + -I- 4- Area of redness and edema exceeding 20 mm. in 



diameter. 

 + ^^ ^ Marked redness, edema and an area of necrosis. 



Doubtful Tliese show redness and traces of edema measur- 

 reactions ing 5 mm- or less in diameter. Redness is 



always regarded as of less significance 

 than edema. 



Long (1934) states that during the past twenty-five years there 

 has occurred a reduction in the incidence of tuberculosis in the 

 United States. He suggests that the antituberculosis campaign 

 which has been carried on for many years is largely responsible 

 for this reduction in the incidence of the disease. 



