HYPERSENSITIVENESS 511 



The smallest dose oi" each that kills within twenty-four hours is 

 determined. The minimum lethal dose of Koch's OT is the stand- 

 ard with which the M.L.D. of the new product is compared. If 

 the latter is larger than the former, then the new product is below 

 standard, while if it is smaller it must be dilnlod 1o correspond to 

 the strengtli of Die old tiil)crculin used as a standard. 



Method of U. S. Bureau ob^ Animal Industry. — Apparently this 

 is also a modification of Koch's method suggested by Schroeder 

 and Brett (1919). Tuberculous tissue from guinea pigs is inocu- 

 lated into a series of normal guinea pigs. As soon as these latter 

 become sensitive to the extent that 0.25 gram of OT per 500 grams 

 body weight will kill 4 out of 6 pigs within twenty-four hours, the 

 remaining pigs are ready for use in standardizing a new product. 

 They are divided into groups of six. Each animal of group I is 

 inoculated intraperitoneally with 0.25 gram of the standard OT per 

 500 grams l)ody weight and each of the other groups is inoculated 

 with a corresponding amount of the tuberculin to be tested. Long 

 says that ' ' a preparation of tuberculin is considered as passing the 

 test if under the conditions of the experiment it kills at least one- 

 half as many guinea pigs as the standard tuberculin, with the 

 characteristic lesions of tuberculin death. ' ' 



Skin Test Method of Lewis and Aronson. — In this method tu- 

 berculin hypersensitiveness is produced in guinea pigs by inoculat- 

 ing intraperitoneally a series of animals, ranging in weight from 

 200 to 300 grams each, with 0.1 mg. of virulent tubercle bacilli. 

 After three weeks they are ready for use in the standardization of 

 tuberculin. They are divided into groups of six and decreasing 

 amounts of a standard tuberculin are injected intracutaneously 

 after the method of Roemer. Each of the other series is injected in 

 a like manner with corresponding amounts of tuberculin of un- 

 known potency. In the series cited by Long the amounts used for 

 intracutaneous injections were 0.02, 0.01, 0.005, 0.002 and 0.001 

 mg., brought up to a total volume of 0.1 c.c. by the addition of a di- 

 luting fluid. The results were read after forty-eight hours and re- 

 corded as 1, 2, 3, or 4, the last named figure (4) indicating the 

 strongest reaction. 



Standardization of Tuberculin by the Precipitation Method 

 OF Dreyer and Vollum. — Immune serum for use in the test is pre- 

 pared by injecting defatted tubercle bacilli in amounts varying 



