1. An examination by bacteriological methods has been made of the antigens present in the washed bacilli of smooth Shiga strains and certain derived variants, including the rough type.

2. The washed formol-killed smooth bacilli kill mice only in massive doses of the order of 5000 millions, suggesting death from protein shock; no protection against a fatal issue is afforded by antibacterial sera. This finding is discussed in relation to recently acquired information obtained by chemical methods on the occurrence of a specific enterotropic toxin in the smooth bacilli, as distinct from the enterotropic toxin present together with a neurotoxin in autolysates of smooth and rough bacilli.

3. Antibacterial sera prepared by immunization with the smooth antigen have high protective value against infection with the living smooth bacilli but not against pure toxin, whereas purely antitoxic sera have no value against infection with the living smooth bacilli.

4. From experiments so far performed, protection against infection with the living rough bacilli has been afforded only by sera prepared from formol-killed rough bacilli and from acetone-killed rough bacilli.

5. From findings reported in (3) inferences are drawn with regard to improvements in the manufacture of dysentery serum for use in man, both prophylactically and therapeutically.

6. The presence of two distinct antigens in the Shiga bacillus has been clearly demonstrated, since the protective values of their corresponding antisera are sharply defined, and do not overlap. The existence of the neurotoxin as a separate entity, unrelated to the smooth ‘endotoxin’, has also been shown by its derivation from a completely ‘rough’ strain, but though the smooth somatic antigen gives rise to a highly protective antiserum, in these experiments it has not been shown, per se, to be a specific toxin.

The writer wishes to thank Sir John. Ledingham and Dr G. F. Petrie for their advice and criticism during this work, and Dr D. W. Henderson, by whom the experiments were first suggested.

The results just described for Greater London compare very favourably with those of similar surveys carried out in the United States by Hopkins & Kelly (1919), Smith (1923), and Layson, Huffer & Brannon (1936) (see also Report, 1934). The figures recorded in Table 7 show that approximately 50% of bottles from the large, the small rotary, and the steam sterilization plants conformed to a standard of less than 600 colonies per pint bottle, or approximately 1 colony per ml. capacity.

The figures for the small rotary plants were not so good as for the large plants, there being a greater proportion of high counts among these. The same was even truer of the steam sterilization plants, in which about a quarter of the bottles were grossly contaminated. The results with the plants using hand-washing only were bad, none of them falling below the 2500 mark.

The general conclusions to be drawn from this survey are that equally good results may be obtained in large or in small rotary plants relying on treatment with hot caustic detergent as in plants employing steam sterilization, and that the uniformly best results are obtained in properly designed and operated plants of the spray type.

It is now realized by a number of workers that the formula which it has been customary to use hitherto for calculating the limits of error of the dose corresponding to a given response (e.g. the median effective dose) or of the result of a biological assay is only approximate. The usual method gives an approximation to the standard error of the logarithm of the dose in question, or of the result, and then uses it in conjunction with the table of the normal probability integral to find the limits of error. The approximation is obtained by the usual statistical method of treating, as Karl Pearson used to say, statistical differentials as mathematical differentials. Bliss (1935) was, I think, the first to realize that exact fiducial limits could be obtained and actually calculated them in a numerical example—but without discussing their theoretical and practical implications. Their mathematical derivation was first published for particular cases by C. Eisenhart (1939) and by E. C. Fieller (1940) in the appendix to his important paper on the biological standardization of insulin. Fieller also gave the general result with a promise (if circumstances allow) to discuss it more fully elsewhere. Later a method for calculating exact fiducial limits was given in the ‘British Standard Method for the biological assay of vitamin D3 by the chick test’ (1940).

It has been shown (Barkworth & Irwin, 1938) that the distribution of coliform organisms in milk follows a Poisson series, and on this basis it should be possible to estimate the population from the results of replicate tests at several dilution levels by reference to tables. In later experiments with water (Barkworth & Irwin, 1941), it was found that the number of positive tubes did not always reach expectation, having regard to the known numbers of organisms inoculated. The peculiar physico-chemical constitution of milk naturally raises the question whether coliform organisms, though present, might fail to give a positive reaction in the presumptive test. It is well known that in favourable circumstances lactic acid bacteria will overgrow all other organisms in milk. In the presumptive test the greatest concentration of milk in routine technique is 1 ml. of milk in 5 ml. of medium. This dilution would not affect the ratio of coliform organisms to lactic acid bacteria. Even when the coliform contamination at the time of testing is ‘present in 0·001 ml.’ the agreement with the fermentation test is only about 50% (Barkworth, 1929). It will be argued that the gas tube would disclose the presence of gas in more cases than the fermentation test, nevertheless it is not perfect, for Chalmers (1928) recovered Bact. coli from plates of 1: 10 dilution of samples of milk which had given a negative presumptive test. There is therefore some reason to expect a small proportion of false negative coliform results to occur with milk samples, and the object of the present experiment was to see if inoculation with a known number of organisms would produce similar numbers of positive tubes in milk and in water.

Some recent advances in the subject of bacterial variation and cytology are:

(1) The white race of Bact. coli-mutabile contains lactase, inhibited by some cause unknown (Deere et al. 1939). Deere (1939) suggests that the cells of the white race may be impermeable to lactose while the lactase system is intracellular.

(2) Variation from non-lactose-fermenter to lactose fermenter in Bact. coli-mutabile takes place on lactose only (Stewart, 1942).

(3) The nucleus of Myxococcus xanthus consists of definite chromatin masses. A process resembling karyokinesis and autogamic conjugation precedes spore formation (Beebe, 1941).

(4) The nucleus of vegetative bacterial cells consists of a pair of dumbbell-shaped chromatinic bodies, which split longitudinally before cell division. The dumbbell bodies are comparable to the chromosomes of animals and plants (Robinow, 1942).

(5) Careful plating provides unquestionably pure lines in the coliform group (Stewart, 1942).

The modern study of the problem of fluorosis (chronic fluorine poisoning) became possible when an Italian, Stefano Chiaie, described, as quoted by Eager (1901), an unsightly dental dystrophy, now known as ‘mottled teeth’. The efforts to trace its aetiology have been ceaselessly continued ever since, mainly by American investigators. Outstanding amongst these were Black & McKay (1916), pioneers whose researches led to the discovery made by Smith, Lantz & Smith (1931) that it was the fluorine, contained in drinking water, in a concentration of not less than 1 part per million (1 p.p.m.) and ingested during the period of calcification of the teeth, which was the direct cause of the dental dystrophy. This result was soon followed up by a number of observers, mainly in the United States under the leadership of the dental profession, amongst them physiologists, experimental pathologists, pharmacologists, veterinary surgeons, geologists and analytical chemists. The gate for further research, which in view of its magnitude and importance must be considered as being still in its infancy, has thus been thrown wide open.