1. Evidence is given that there exists a multiplicity of serological groups of B. diphtheriae.2. Ten of these groups have been studied in this communication.3. Into these ten groups could be placed all except 16 of 348 strains of virulent B. diphtheriae investigated.4. A description of the technical difficulties encountered is included in the hope that this may prove of service to other workers.Some evidence on the antigenic structures of different strains is advanced.5. The application of this method of investigation to the problems of epidemiology is briefly discussed, and evidence of its value brought forward.

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Experiments I–VIII.I shows that under the conditions shown the plates were covered with innumerable colonies 7 feet above ground level to ground level. The beds and trestles were used to keep the hut always uniform.II shows that 8 feet above ground, i.e. on top of the crossbeams, the same conditions obtain.III, IV, V, and VI show that the same condition exists in the area between the beds or trestles. The beds make no difference, better or worse.VII shows practically the same condition high up on the beam between the beds. The inverted plates naturally show less colonies, as the organisms mostly fall on to the plates.VIII confirms the above.There is only one conclusion to draw from these experiments, and that is that practically speaking there is no difference in the number of organisms on the ground floor and 8 feet above it, in the ordinary men’s sleeping huts, Barrack Design 230/14.

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