HYPERSENSITIVENESS 513 



Tlie result of Koch's test does not establish a unit: it is quanti- 

 tative only in a ''pass or fail" manner. Long states that the test 

 will not differentiate between two preparations of tuberculin, 

 one of which might be twice as potent as the other. While the 

 PYankfurt method attempts to avoid this criticism, it does so only 

 by introducing an extremely "laborious process of comparison 

 with a standard tuberculin on a large series of animals." Al- 

 though the test employed by the United States Bureau of Animal 

 Industry is superior in certain respects to other ' ' lethal dose tests, ' ' 

 it too requires a large number of animals and is also quite laborious. 

 Long calls attention to the fact that while a test of this type estab- 

 lishes a "standard which must be met before a tuberculin is ac- 

 ceptable, it does not establish a unit which can be used in 

 measuring doses." 



Advantages and Disadvantages of the Various Tests. — 

 Criticism of the intracutaneous test. 



1. The technique is simple and economical of both time and 

 animals. 



2. It would seem more logical to standardize in respect to the 

 skin allergy of a test animal since the product is to be used to 

 determine the skin allergy of patients. 



3. Long and others feel that one serious objection to the test is 

 that in a series of tuberculous guinea pigs the reactive capacity 

 of the skin varies tremendously. On the other hand, Seibert and 

 Munday (1932) find that when one pound guinea pigs are inocu- 

 lated subcutaneously with 0.1 mg. of strain H37, they develop 

 quite uniform skin sensitivity. In regard to the standardization 

 of tuberculin they say "since it is possible to obtain consistent 

 results in sensitive tuberculous guinea pigs by means of the in- 

 tracutaneous test, and since the chief use of tuberculin at present 

 consists in diagnostic skin reactions, it is advisable to base the 

 standardization, so far as possible, upon the intracutaneous test 

 as has been maintained by Aronson (1926), Okell and Parish 

 (1927) and Funk and Huntoon (1930)." 



Criticisms of the complemetit fixation and precipitin methods. 

 The chief objection to both of these methods of standardizing 

 tuberculin is that neither complement fixing nor precipitating 

 antibodies are known to be involved in the tuberculin reaction. 



