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The Cyprus strain of bluetongue virus was successfully transmitted through six passages and the Station strain through one passage in calves. Although the animals developed no visible evidence of infection, viremia as shown by both passage and fluorescent antibody examination of infected foetal bovine kidney culture, and by serological conversion was nevertheless demonstrated. No enhancement of virulence for calves or sheep was shown following bovine passage. A ewe inoculated in late pregnancy with blood drawn from a calf 59 days after its infection, gave birth to a lamb from whose blood the virus was isolated. Significant complement-fixation titres persisted for at least 200 days.

The fluorescent-antibody technique was employed for the detection of bluetongue virus in bovine foetal kidney cell cultures inoculated with tissues and blood from experimentally infected animals. In the first series, a total number of 79 inoculated suckling-mouse brains were examined, 36 as frozen sections alone and 43 as impression slides in conjunction with tissue culture inoculation of the same material. With the combined tissue culture immunofluorescent methods, 36 suspicious were detected by impression smears and 37 positives by the tissue culture out of 43 brains examined. Twenty-two were suspicious out of the 36 examined as frozen sections. Results obtained with the second series, using sheep tissues, showed that the combined tissue culture-fluorescent antibody method was satisfactory for demonstrating the virus in blood of infected animals 1 to 9 days postinfection, and in some organs after death. No false positive reactions were obtained.

The complement-fixation test used at Onderstepoort was compared with the method used at A.D.R.I. on infected calf and sheep sera. In the first method, the tests are incubated at 37 degrees C for 90 minutes and the test sera are inactivated at 53 degrees C; whereas in the A.D.R.I. method, the test sera are inactivated at 60 degrees C for 30 minutes, incubation is at 9 degrees C for 18 hours, and guinea-pig complement is supplemented with 5 per cent fresh, non-inactivated, normal calf serum. Serial serum samples from one of six experimentally infected calves were negative in the Onderstepoort test, three calves gave only trace reactions and two showed maximum titres of 1:10 whereas all six had maximum serum titres of 1:10 to 1:80 in the A.D.R.I. test. A good correlation was obtained, however, between the results of the two methods with the sera of experimentally inoculated sheep although titres 3 to 8 times higher were obtained with the A.D.R.I.'s test. Post inoculation bleedings from each sheep reacted in both tests.

Sera of sheep and calves infected with the California type 10 and Cyprus type 3 viruses of bluetongue were tested by the regular and modified direct complement-fixation tests. To obtain satisfactory complement fixation it was necessary to use the latter test. Cross reactivity was found, therefore, the California type 10 antigen could be used in testing sera of animals infected with the Cyprus virus.