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PART I. VARIOLA AND VACCINIA IN spite of the voluminous literature, much of it of a polemical rather than scientific nature, on the immunity relationships between variola and vaccinia, comparatively little work has been carried out on experimental animals, and the results of different workers are not altogether concordant. Even in the important article by Blaxall (1930) in the System of Bacteriology only a few lines were devoted to a discussion of the existing experimental evidence, and also in the more recent article by Gastinel (1938) this particular problem has been very briefly treated. PRESENT EXPERIMENTAL WORKOpportunity was taken during an outbreak of virulent smallpox in the Gezira cotton-growing area of the Anglo-Egyptian Sudan in 1938 to collect variolous material from different patients, and to inoculate a series of monkeys. TECHNIQUEThe contents of the vesicles or pustules were aspirated into capillary tubes, which were immediately packed in ice in a vacuum flask and brought directly to Khartoum, 80 miles from the epidemic zone. The capillary tubes with the pus were ground up in a mortar with distilled water (pH 7.0), the suspension lightly centrifuged to throw down the powdered glass, and the turbid supernatant fluid pipetted off and stored in the freezing chamber of a refrigerator. Inoculation was made on to the scarified bellies of monkeys (Cercopithecus sebaeus), the amount of inoculum and area varying in different animals, and the subsequent immunity tests were carried out with both vaccinia and variola.Details of the treatment of each animal are given in the following notes:

1. The more recent literature on the experimental methods employed in variola or alastrim-vaccinia variation is reviewed and briefly discussed.2. An account is given of attempts to produce a vaccinia variant from variola of the virulent type and a successful result, by employing the method of intratesticular passage, has been described.3. The reasons for accepting this as a genuine variation and not a vaccinial contamination are discussed.4. An attempt has been made to analyse some possible factors underlying the discrepancies in the literature, and a plea is made for more co-operation in future work on the subject.

a series of sporadic cases of enteric fever in Khartoum during the latter part of 1934 and 1935 afforded an opportunity of examining certain claims advanced in these papers. As the following observations on various aspects of the subject have been carried out over a period of 18 months the results are inevitably somewhat scrappy, but in view of the importance of the subject it was thought that they might not be altogether without interest for other workers.As a strictly chronological record would be somewhat confusing the results obtained are grouped under the main points investigated.When the work was commenced no inagglutinable cultures of local strains of B. typhosus were available, and such cultures were kindly supplied by Dr A. Felix and Major H. J. Bensted, to both of whom the author is much indebted for their assistance. PRESERVATION OF CULTURESTo avoid as far as possible too many subcultures, the method of infected mouse spleen dried in vacuo over calcium chloride as recommended by Perry et al. .(1934) was followed, the only difference being that the white rat was used in place of the mouse, the latter not being available. It may be stated here that young white rats seem to be equally susceptible to virulent strains of B. typhosus as mice. The method has given excellent results, the claim of these authors that cultures could be obtained after 4 months being confirmed, and when tested on young rats the organisms seemed to have lost none of their virulence and inagglutinability by 0 serum. As no ascitic fluid was available, Kauffmann's method (1935b) of passage of cultures through complement and growth on fresh ascitic agar was not tried, but it seems to offer no particular advantages at least to workers in dusty tropical countries. Where no mention otherwise is made all agglutination tests were carried out with lving suspensions in saline from agar cultures of 18-20 hours old. The macroscopic technique was used in all agglutination tests, incubation being carried out in a water bath for 4 hours at 370 C. and the results were read after standing at room temperature for 22-24 hours.

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