Report on the examination of samples of veterinary tuberculin / by R.A. O'Brien.

  • O'Brien, Richard Alfred, 1878-1970.
Date:
[1925?]
Catalogue details

Licence: In copyright

Credit: Report on the examination of samples of veterinary tuberculin / by R.A. O'Brien. Source: Wellcome Collection.

    3/4 (page 3)
    giving a false idea of the accuracy of the method (v. Eagleton and Baxter, loc. cit., p. 295), which is not comparable with that attained in the titration of diphtheria toxin and antitoxin. We are at present of opinion that a tuberculin whose real value can be represented as 100 might be returned, as the result of a single test, as of any value between 60 to 140, i. e. 40 per cent, above or below its proper value, but that in a laboratory where constant controls are in use, in a series of tests on a tuberculin whose real value is 100, the mean values obtained from the tests would closely approach 100, and the extreme values obtained might be 75 to 125, i. e. 25 per cent, above or below the proper value. In Column 2, tuberculins which were equal to a tenfold dilution of Standard Tuberculin are given a potency figure or ‘ percentage ’ of 100 and the figure for the others calculated on this basis. Column 3 shows the average dose indicated for a full-grown animal in the literature accompanying the samples. Column 4 shows the amount of Standard Old Tuberculin con¬ tained in the dose indicated. For convenience this figure has been translated in Column 5 into a ‘ percentage 100 being assigned to those tuberculins which were equal to a tenfold dilution of Standard Old Tuberculin and which were to be given in the average dose of 4 c.c. generally used by veterinary practitioners. Comments. The only comment which it seems permissible to make on these results is that, whatever deviation from the standard may be allowable, the laboratories issuing A, L, M, N, and P, if they were aware of these results, would probably wish to conform to the common standard. This remark particularly applies to A, N, and P, since with A, which is apparently made by diluting Old Tuberculin five times instead of ten as practised by most makers, ‘ doping ’ or 4 plugging ’ of cattle presumably becomes much easier to carry out; on the other hand, the veterinary surgeon using P or N may easily fail to detect tuberculosis in an animal. The samples submitted did not permit an investigation into the constancy of strength of successive batches of tuberculin issued from the various laboratories. We have reason to believe that the degree of constancy is fairly satisfactory in most cases, but we have evidence that this is not so in all.