NASHVILLE May igj8 IX '5 or 'The natural history of (infectious disease, cancer, war, woman or what not) '. I have always been fascinated by the simple concepts of biology-reproduction, mutation, sexual redistribution of characters and selective survival-and how the interactions of species and ecological communities can be brought into a comprehensible pattern in the light of those concepts. Particularly for the problems of infectious disease in the Surely, here we find also a situation where clones of cells flourish and wane in very much the same fashion as bacterial to produce and liberate /?-galactosidase. At low concentrations of inducer the primary induction of permease is slow, but, wherever this is accomplished, the bacterium involved takes in a relatively large amount of inducer which can now maintain the production of permease and induce y^-galactosidase production both in itself and in its descendants. Bacteria which have not yet been rendered permeable are not induced. Such a population is composed of two sorts of bacterium : fully induced and not induced. This can be shown by choosing a ' maintenance concentration ' of TMG (5xio~^m) which for pre-induced bacteria will allow full synthesis of adaptive enzyme but has only a negligibly small power to induce normal bacteria. If limit-'Classical circulating antibody' is, however, far from being the only product of specific response by the body to antigenic material and it is, possibly, not even the most important.

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In previous papers we have described (Burnet, McCrea and Stone, 1946) the activity of filtrates from Y. cholerae in removing "virus receptors" from red cells. Cells so treated also develop the condition of panagglutinability described by Thomson (1926) and Friedenrich (1928) and evidence has been given that both effects are due to the action of an enzyme which for convenience we refer to as receptor-destroying enzyme, RDE. In the second paper (Stone, 1947) of the series, it was shown that except for minor details the action of viruses of tlie influenza group on the red-cell surface was essentially the same as that of RDE.The present paper reports further work which has been directed mainly, toward determining the optimal conditions for the production of enzyme by the vibrio, and for the preparation of purified material by elution from red cells. EXPERIMENTAL. Tlie Production of BDE.In the work reported previously, EDE was prepared by the growth of a suitable V. cholerae strain in nutrient broth for 16-20 hours. Filtrates from such cultures gave titres of the order 3.60-240. Growth in simple peptone water, though producing similar degrees of turbidity, gave only very small yields (<30).Much higher titre filtrates could be obtained by the method used by one o-f us in 1930 for the production of staphylococcal toxin (Burnet, 1930). Plates of weak (1 p.c.) nutrient agar wero inoculated with a few drops of broth culture of the desired strain and incubated for 16 hours at 37° 0. The surface growth was scraped ofE with a glass rod and the agar removed into a gauze bag inside the top of a Buchner funnel. Usually a batch of 20 Petri dishes waa used. The gau^e bag waa tied and the rfluid pressed out by a weighted cylindrical jar fitting closely into the top of the Buchner funnel. The expressed fiuid was centrifuged if necessary and paBsed through a Seitz filter. These "agar filtrates" had a pH between 7-5 and 8-5. Their RDE titres with suitable strains ranged from 320 to 2,000, and the method has been used as a routine both for the production of EDE and also for the desquamating enzyme described elsewhere.A second effective method is growth of a suitable strain in the allantoic cavity of 12-day chick embryos. Death occurs with a small inoculum in approxima.tely 24 hours and fluid harvested at this time and centrifuged gave titres of almost exactly the same range, 400-2,000, as those obtained with agar filtrates.

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