The early literature on the specificity of the immunological types of foot-andmouth disease virus included references to minor antigenic differences which occurred between strains of virus of the same type. Such strains were called variants. The value of these observations, however, was limited by the techniques then available for differentiation. Bedson, Maitland & Burbury (1927) applied an in vitro serum neutralization test in their comparison of two strains of virus of Type A. They recorded results which indicated that higher serum neutralization titres were obtained with homologous serum-virus mixtures than with heterologous mixtures.Progress in this field of investigation resulted from the development of the complement fixation test. Traub & M6hlmann (1946) used this test to demonstrate antigenic differences between three strains of virus of Type A and also drew attention to the possible significance of these observations in relation to the efficiency of protection by vaccines. Subsequent work at this Institute was directed to the correlation of the results obtained by cross-vaccination, cross-serum neutralization and cross-complement fixation tests. In the first of these experiments Galloway, Davies & Smith, 1962;Hyslop, Davie & Carter, 1963; and unpublished work) has confirmed that there are strains of virus of the same immunological type which can be classified as antigenic variants or subtypes within the types and that in general there is good correlation between the results of the three tests. The results of the two serological tests and the cross-vaccination tests showed that three of the ten pairs were of the same subtype and that seven of them were dissimilar.It has been found that the reproducibility of the results obtained in the complement fixation test and its convenience are of advantage when a large number of strains of virus of one type have to be examined. The complement fixation test was applied by Traub & M6hlmann (1946) to demonstrate differences in the titre of immune sera reacting with homologous and heterologous antigens. used the amount of complement fixed as a measure of such reactions, while Graves (1960) combined the titration of complement with the titration of antisera in order to compare homologous and heterologous antigen-26 Hyg. 62, 4

Antigenic differences between the strains RV 11 and SA 13/61 of foot-and-mouth disease virus (type SAT 1) were studiedin vivoby cross-protection tests. Cattle inoculated with formolized antigen of either strain developed good immunity to experimental infection with the identical strain but little resistance to the other strain.In vitrothe results of complement fixation tests and of serum-virus neutralization tests in tissue culture were consistent with the observations madein vivo. The results of studies on the serological relationships between four strains of type SAT 1 are presented.The importance of strain differences in the epizootiology and control of the disease is discussed briefly.The authors wish to thank Dr I. A. Galloway and Dr J. B. Brooksby for their advice and criticism, and to acknowledge the valuable technical assistance of Mr K. Herniman, Mr R. L. G. King and Mr E. Scoates.

The engineering properties of deep continental margin sediments were determined on a worldwide basis. Deep Sea Drilling Project (DSDP) core data and material were utilized from over 900 cores obtained from 89 sites, primarily on the continental margins. Cores were recovered from penetrations to 200 m in water depths averaging 3000 m. Supplementary laboratory testing on selected cores was directed toward determining index properties and shear strength properties of the sediments. The study included a literature review of deep-sea soil properties, the results of which are to be used by DSDP to evaluate foundation conditions for reentry cones with long casing strings. The results will also be used for a feasibility study of an ultradeepwater marine riser and wellcontrol system. The marine sediments examined can be divided into three main types: clay, calcareous ooze, and siliceous ooze. Sediment distribution consisted of 48% calcareous ooze, 43% clay, 6% siliceous ooze, and 3% volcanic ash. Because of the sample disturbance inherent in the deepwater coring operation, emphasis was placed on analyzing sediment properties not significantly affected by changes in in situ stresses and structure caused by sampling. Averages and ranges in values of water content and unit weight are presented for the three main sediment types. Plasticity and strength characteristics are discussed in detail and the elastic and compression properties are outlined. The geotechnical properties of deep continental margin soils are summarized.

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