1. Disinfection curves obtained from data on the action of phenol on Bact. coli at 35° C. under conditions such that unfavourable circumstances, other than the presence of the germicide, were as far as possible eliminated, have been used for the calculation of the concentration exponent for phenol, i.e. n in the formula Cn x t = K. The death-rate was not constant throughout the germicidal process but showed initially a phase of slow but increasing death-rate which merged gradually into a phase which was treated (for reasons given) as one of constant rate. This was also the maximum rate for any given phenol concentration.

2. The virtual sterilization times (v.s.t.'s), i.e. the times in min. required for the mortality to reach 99·999999 % as determined by slight extrapolation of the log survivors-time curves, the 99·9 % mortality times and the 99 % mortality times could all be used for the calculation of values of n for phenol as they all gave satisfactory linear relations between log concentration and log time.

3. The 50 % mortality times did not show a satisfactory linear relation between log phenol concentration and log time over the full concentration range, and at this mortality level the concentration exponent appeared to increase for concentrations above 4·62 g. phenol per 1.

4. The value of n varied according to the mortality level chosen. It was 5·8421 ± 0·1876, 6·6062 ± 0·2034 and 6·9638 ± 0·2164 when the v.s.t.'s, 99·9 % mortality times or 99 % mortality times were used. The differences between the first and second and first and third values are significant, but that between the second and third values is not. The value calculated from the v.s.t.'s is regarded as being the most important.

5. Evidence was obtained that, as expected on theoretical grounds, n increases for very low concentrations of phenol. If the aberrant value obtained at the lowest phenol concentration be omitted from the calculations, the value of n calculated from the v.s.t.'s becomes 5·6588 ± 0·1422, but the decrease is not significant.

6. The maximum death-rate was related to the phenol concentration according to the expression km = 9·1743 × 10−6C5·0752, where km is the maximum (logarithmic) death-rate per min. and C the concentration of phenol in g. per 1.

1. Data on the maximum temperatures of growth of certain organisms, on the rate of toxin production by Cl. botulinum and the rate of multiplication of certain Salmonellas, is given, as a basis on which to define the time and temperature of dehydration in the preparation of dehydrated foods.

2. It is concluded that 50° C. is the minimum temperature below which dehydration should not be carried out. Where some heating below this temperature is unavoidable, the period of such heating should not exceed 4 hr.

3. Data on the microbial changes in dehydrated foods equilibrated at various humidities indicate that bacterial growth is not expected below about 15 % water content. Some experiments on the death of bacteria at water levels below this are discussed.

4. Details are given of the general bacteriological examination of the process of dehydration on a commercial scale for dried soup, dried minced beef, dried carrot, cabbage and potato.

This work was carried out under the joint auspices of the Food Investigation Board of the Department of Scientific and Industrial Research, and the Ministry of Food, and is published by permission. The authors are indebted to Professor H. R. Dean for the provision of facilities, and to him, Professor G. S. Wilson, Dr A. W. Downie, and various other members of the Emergency Public Health Laboratory Service for help and advice.

During the last year further investigations of germicidal mists, especially those produced by heat-volatilization of phenols, have been carried out. We are primarily interested in continuous disinfection of the air in the presence of man, and all our original experimental results appeared to show that a small quantity of the higher phenols in the mist form was more potent to bacteria than when in the vapour form. Thus, persistence as a mist long enough to ensure a duration of lethal effectiveness covering the time taken for at least one air turn-over was considered to be a desirable characteristic of a germicide to be used for our purpose.

1. The problem of assessing nutritional state

This paper emphasizes the need for measurement in diagnosis and recognizes two distinct problems, those of:

(a) Diagnosing specific diseases in the sense of distinct pathological conditions.

(b) Assessing general malconditions where there is no sharp dividing line between the normal and the subnormal.

It suggests a programme of research designed to overcome some of the difficulties inherent in (b) in the case of nutritional assessment.

2. Establishing general health standards

The first requirement is the scientific standardization of the elements making up the concept of health and good physique. This is a complex matter requiring all the help which statistical procedures can give. Moreover, we must check the reliability of the assessors and the indicators which they use before we can place any reliance on results purporting to relate to the population studied.

Provisionally we begin by collecting a battery of indicators of general health; each is then given a graded assessment for each child (and the assessment is repeated to obtain its reliability), and by employing the statistical device of factor analysis we can determine what combination of symptoms will give the highest agreement with the criterion of general health abstracted from these individually imperfect measures. We are actually making explicit the stages which are normally telescoped in the method of ‘general impression’ (which is the method usually adopted in assessing general health, state of nutrition, etc., despite evidence of its unreliability). In this method a number of individual characteristics are fused together without ensuring that different observers will attach equal importance to the signs or even that they will take into account the same ones. The emphasis to be given to each symptom in the final mark is determined statistically by its agreement with the aggregate result. Some indicators may give results so unrelated to the others that they must be eliminated. Other tests, whether physiological, functional or anatomical, may later be added to the battery to reinforce it. A point of practical importance is that some readily assessable symptom or index may be found which gives results in close enough agreement with those of the standard battery to enable it to be used as a substitute, thus shortening the task of diagnosis without appreciably lessening its accuracy.

An alternative criterion could, as we have seen, be the weighted combination of doctors' assessments, for by weighting the results according to each doctor's agreement with his colleagues we were able to increase the agreement between the team result and the hypothetical true mark. However, since the ordinary methods of assessment are unreliable, even the pooled results of the team do not give as good a standard as the standardized battery of tests.

A third standard is sometimes possible in the form of an objective accurately measurable physiological laboratory test or anatomical index. If this is inconvenient to apply generally, any single symptom or pool may be tested by correlation with it to see if the agreement is close enough for practical purposes.

3. Study of more specific nutritional defects

Factor analysis can be used to discover and assess more limited similarities than those covering the whole range of observers or test symptoms. For example, the doctors tended to show group affinities (depending possibly on their different emphasis in diagnosis) in addition to their somewhat low general conformity. Applying similar analytic methods to the study of symptoms, we might isolate specific nutritional deficiencies or it is possible that group factors may be revealed corresponding to the effects of recent or early adverse nutritional conditions respectively.

Whilst the examples of analytic techniques have here been applied to illustrative cases in nutritional and general health assessment, they are equally applicable to other fields of medicine, in particular to endocrinology and to the study of predisposing conditions of disease.

My thanks are due to Prof. Burt and Dr E. H. Wilkins for their suggestions for modifying my original draft. However, this in no way commits them to agreement with the views expressed here.

[Note added in Proof.] Since writing this article I have had an opportunity of correlating and analysing some results of nutritional surveys involving clinical and biochemical signs of malnutrition. The evidence so far obtained indicates a rather weak general factor for clinical signs identifiable with general nutritional state. I hope to be able to give the full results when the material becomes available for publication.

Like the skin and its appendages, the teeth, nails and hair, so also other tissues of ectodermal origin are here shown to be affected by fluorine. The action of fluorine consists in lowering the level of the calcium in the blood and tissues. The epithelia of the mouth and the salivary glands, of the nasopharynx, the conjunctivae and the lachrymal glands may be affected. Signs and symptoms are thus produced which are closely similar to those usually attributed primarily to infection. It is suggested that an infection accompanying chronic fluorine poisoning is of a secondary nature, and that it is brought about by the loss of calcium in the body.

Dystrophies due to chronic fluorine poisoning in organs regulated by the parathyroid glands, namely the skin and its appendages, the nails, teeth and hair, and also in bones, are here shown to be unusually common in this country. They should be regarded as easily detectable signs of a serious disturbance of the calcium metabolism of the body. Fluorine is a poison of which the action, in many respects, is similar to that of arsenic. It is the task of the authorities responsible for the health of the nation to search for ways and means capable of minimizing its effect.

I wish to express my sincere thanks to the Librarian of the Royal Society of Medicine and his staff for their never-failing courtesy and help.

During the discussion following the late Sir Henry Japp's paper on ‘Prevention of compressed air illness’, read at a meeting of the Institute of Structural Engineers on 28 March 1935, I suggested an extension of Haldane's system of decompression which might prove of considerable practical value in tunnel and caisson work (Japp, 1935). Briefly the proposed extension consisted in making use of Dalton's theory of the partial pressure of gases in such a manner that denitrogenization of the blood might be brought about while the workers were still under full pressure, namely, by making them breathe before entering the decompressing chamber an artificial atmosphere containing no nitrogen.

Results are given of the typing (by biochemical fermentation tests) of 290 strains of Bact. paratyphosum B isolated during an epidemic in the north of Scotland. Of these strains 283 were of type R3I1. Seventy-four strains isolated in or around Edinburgh later in the same year, and 107 strains from three patients were also typed. Some variation (2·4 % in the north and 4 % in Edinburgh) was observed, but, in general, typing by the fermentation of rhamnose and inosite is of epidemiological significance.

I am indebted to Dr Kirkpatrick for supplying strains of Bact. paratyphosum B and providing access to the necessary records, to Dr Seiler for epidemiological notes on the Edinburgh cases, and to Prof. Mackie for his valuable advice and encouragement.

1. The basic observations of Piekarski (1937–40) and F. Neumann (1941) on Feulgen-positive, chromatinic structures, going through a regular cycle of division, in the cells of Bact. coli and Proteus vulgaris are confirmed and the view that these structures are nuclear in nature is accepted.

2. The chromatinic structures in bacteria from old cultures, although usually distinguishable from the cytoplasm, are too small to be resolved accurately. After transfer to a fresh nutrient medium the chromatinic structures increase in size and give rise to short, often dumbbell shaped, rods (chromosomes) which multiply by splitting lengthwise in a plane more or less parallel with the short axes of the bacterium.

3. The chromatinic structures of Bacl. coli and of Proteus vulgaris are essentially the same as those previously described in myxobacteria and actinomycetes (Badian, 1930, 1933, 1936) and in various well-known aerobic spore-forming bacteria (Badian, 1933, 1935; Robinow, 1942).

4. A single cell of Bact. coli or Proteus vulgaris contains one chromatinic body or one or two pairs of these, representing primary and secondary division products.

5. Few bacteria from young cultures are single cells. When fixed through the agar with Bouin's mixture and stained briefly with Giemsa's solution, bacteria from young growing cultures of Bact. coli, Proteus vulgaris, B. mesentericus and B. megatherium assume a banded appearance indicating that each bacterium consists of two, three or four separate cells.

6. A plasmolysing treatment has been applied to B. megatherium which provides direct proof of the composite structure of this bacillus by inducing its component protoplasts to shrink away independently from the outer supporting cell wall.

I wish sincerely to thank Dr H. B. Fell for the hospitality offered to me at the Strangeways Laboratory, for her sustained interest in this investigation and for her help in preparing the manuscript for the press. I have also pleasure in admitting my indebtedness to Prof. E. G. Pringsheim for much helpful criticism and advice in matters relating to the bacterial cell wall.

Homogenization of activated sludge greatly increased the apparent bacterial count obtained by plating on a solid medium, and for this reason facilitated the isolation of the predominant flora by liberating the bacteria from the interior of the sludge flocs. The ordinary domestic cream-making machine was found to be quite effective for this purpose.

The high counts obtained indicated that there are probably several hundred thousand million bacteria per gram of dry matter in activated sludge.

Aeration of sewage was found to result in an increase in the total count of bacteria, and a high count was maintained for a considerable time. After aeration for several days fairly rapid and apparently fairly complete separation of the sludge occurred on allowing the liquid to stand, but the supernatant liquor contained large numbers of bacteria. When a fresh quantity of sewage was added to the small quantity of sludge which settled and a second period of aeration commenced, the bacteria were found to associate more quickly with the sludge than they had during the first aeration. Coliform bacteria and spore-forming aerobes formed only a small fraction of the total number of micro-organisms concerned in these changes, and moulds and yeasts never accounted for a large proportion. The predominant bacteria did not produce acid from glucose.

Various media were tested in investigating the bacteriology of activated sludge. None showed any superiority to nutrient agar. Coliform bacteria and aerobic spore-formers were encountered in negligible numbers. The morphological and physiological characters of seventy-one strains of the predominant bacteria were determined. The majority were Gram-negative rods with no action on carbohydrates and were members of the genera Achromobacterium, Chromobacterium, and Pseudomonas. Those isolated from activated sludge soon after its formation from aerated sewage were found to be non-proteolytic, but a proteolytic flora was established after the sludge had been built up for a period of 4 weeks. The characters of the predominant bacteria indicate that they are water types derived from the water supply or the drainage water which enters sewage. Intestinal bacteria appear to be unimportant.

The experiments described in this paper were carried out as part of the programme of the Water Pollution Research Board of the Department of Scientific and Industrial Research, and the results are published by permission of the Department.