*For the subcutaneous test 2 to 4 cc. of Koch's Old Tuberculin 10 per cent was used. Temperatures after injection were taken at two hour intervals from the eighth to the twentieth hour. In herds 6, 10 and 13 it is unfair to judge the results from the subcutaneous test without considering the possibility of a modifying effect from the intradermal test just previous. We believe that the above results should be interpreted as indicating that the two tests are about equal in accuracy. The results reported in tables A, B, and C are all by European observers and the proportion of reacting animals in which no lesions were found is much larger than has been reported by inspectors in the United States. As we do not know under what conditions these tests were performed no comparisons can be made with the results which we have obtained. Klimmer and Wolff-Eisner" in their handbook of Serumtherapie and Serumdiagnosis have published the following tables which are of interest in a consideration of the intradermal method. It is possible that some of the figures in these tables were misprints, as the additions and percentages do not check in all cases. RESULTS OF VARIOUS FORMS OF THE TUBERCULIN TEST ON TUBERCULOUS CATTLE A positive cutaneous reaction occurred in 39 out of 141 tuberculous cattle or 28% 38 out of 143 tuberculous cattle or 27% A positive intradermal reaction occurred in 249 out of 315 tuberculous cattle or 79% A positive vaginal reaction occurred in 51 out of 66 tuberculous cattle or 77% TABLE C RESULTS OF VARIOUS FORMS OF THE TUBERCULIN TEST ON CATTLE IN WHICH NO LESIONS WERE FOUND ON SLAUGHTER A positive cutaneous A positive dermal reaction occurred in 6 out of 125 cattle or 5% A positive intradermal reaction occurred in 47 out of 252 cattle or 19% RESULTS OF RETESTS On retesting by any form of the tuberculin test, a badly infected herd, from which all the reacting cattle have been removed, it will usually be found that from 1 to 30 per cent will react. This is not necessarily due to the failure of the previous test, because the cattle may in the meantime have become infected from contaminated pastures or other sources. Another reason for the reaction of such cattle on retest is the fact that cattle often do not react during the incubation of tuberculosis or while the disease is latent and the lesions encapsulated. In a badly infected herd many animals may be so recently infected that sensitiveness to tuberculin has not developed. In tuberculosis this period of incubation is variable. In some cases the disease probably begins to progress on the day of infection; in others the germs may be lodged in the tissues for a long time before lesions actually develop. The arrest of the disease and encapsulation of the lesions is of frequent occurrence in the tuberculous cattle. This accounts for the fact that cows which have reacted occasionally fail to react when subsequently tested. Later the disease may start up and then, on a third test, the animals may again react. The commission appointed by the American Veterinary Medical Association have recognized these facts in their recommendation that herds over 50 per cent of which give positive reactions be handled, as far as eradication of the disease is concerned, as though all the herd had reacted. The well-known fact that animals in advanced stages of the disease frequently do not react applies equally to the intradermal and subcutaneous methods, but from our observations we think the former will detect more arrested or latent cases. The results in retesting compare favorably with those we have obtained with the subcutaneous method under similar conditions. The following data showing the results of retests is typical of what is to be expected. TESTS FOR DAIRY COMPANY B Sept. and Oct., 1913. Tested by the intradermal method, 2184 cattle, 775 reacted, 35.5 per cent. (Three hundred of the non-reactors were segregated on one ranch and four months later 228 of them were retested; 176 of the reacting cattle were also retested in four months.) Retested 228 non-reacting cattle, 46 reacted, 20.2 per cent. Retested 176 reacting cattle, 173 reacted, 98.3 per cent. Feb., 1913. Feb., 1913. Following are the results of frequent subcutaneous tests in three In the last three dairies the reacting cattle were at once removed and the barns were frequently disinfected. Additions to the herd were non-reactors selected chiefly from infected herds. In the case of the cattle belonging to Dairy Company B the non-reacting cattle were separated from the reacting, but thorough disinfection was impossible. Since the conditions in the various dairies differed materially, no comparisons between the intradermal and subcutaneous tests are justified. DESCRIPTION OF CASES WHICH REACTED TO THE INTRADERMAL BUT DID NOT REACT TO THE SUBCUTANEOUS TEST The following detailed history of ten cows which reacted to the intradermal but not to the subcutaneous test is submitted as proof that cattle, having latent, slight or inactive lesions of tuberculosis, may fail to react to the subcutaneous test, but may react to the intradermal. Except when otherwise stated, all tests in these cases were made with Koch's old tuberculin, dilution 1 to 10 of physiological salt solution. The dose for the intradermal tests was 15 cc. The dose for the subcutaneous tests varied from 2 to 4 cc. COW 1. Peggy. Grade Holstein. Good physical condition throughout the time she was under observation. Oct. 10, 1911. Mar. 2, 1912. Apr. 2, 1912. July 20, 1912. Oct. 4, 1912. July 10, 1913. July 12, 1913. Tested by subcutaneous method. No reaction. Tested simultaneously by the subcutaneous and intradermal Tested by the intradermal method. Strong reaction. Tested by the intradermal method, using cc. of 10 per cent COW 2. Ear tag No. 1649. Fair physical condition. May 6, 1913. May 8, 1913. June 6, 1913. June 23, 1913. June 26, 1913. Tested by intradermal method. 35 per cent O. T. tuberculin. Tested by subcutaneous method. No reaction. Tested by ophthalmic method. No reaction. Tested by ophthalmic method. 2 per cent purified tuberculin. Tested by the intradermal method. 1⁄2 per cent purified tuber- |