When individual responses in a biological assay show considerable variation associated with the values of a concomitant variate, covariance analysis may be used in order to adjust the mean responses and to improve the precision of the assay. Usually this is preferable to the choice of an adjustment which involves an arbitrary assumption about the effect of variations in the concomitant variate on the measured response. Published accounts of the process are open to certain theoretical objections, though they may be sufficiently exact for most practical purposes.

The present paper describes a method of calculating the relative potency, and its precision, which may be a little more laborious, but which is in full accord with standard statistical practice. The computations are illustrated on data from a prolactin assay by the pigeon crop-gland technique, in which the final crop-gland weight showed a positive correlation with the body weight at the start of the assay. The results are compared with those obtained either from the unadjusted crop-gland weights or from these weights expressed as proportions of body weights. The covariance method leads to a more precise estimate of the potency of the test preparation than do either of the others; there is evidence, however, that the increase in precision will not necessarily be large unless the correlation between the response and the concomitant variate is very close.

In a final section, the full statistical tests of assay validity in the covariance analysis are described; these are lengthy, and fortunately are required only when the validity is in considerable doubt.

The methods of adjustment have been described in this paper with respect to an assay depending upon parallel regression lines of responses on the logarithms of doses. They may be adapted for use with ‘slope-ratio’ assays (Bliss, 1946; Finney, 1945; 1948; Wood & Finney, 1946), in which the regression of response on dose itself is linear. So far the need for adjusting for concomitant variation in these assays seems not to have arisen, and discussion of computational details may be postponed until the need is felt.

The studý of the Fusiformis necrophorus culture ‘132’ showed that new pure LI cultures could be isolated from it, which have already been maintained for one year and undergone more than 100 passages without reverting to their original type. The new cultures resemble the old L 1 strains from Streptobacillus moniliformis in every respect except for their strict anaerobiosis. It has been observed that swellings of the bacteria develop into large bodies not distinguishable from the elements of which the pure L 1 culture consists.

In the light of the new observations on Fusiformis necrophorus which are in full agreement with those of Dienes & Smith it is still not possible to disprove the symbiosis theory, for the newly established L 1 cultures have not reverted so far. Secondly, though it has been seen that L 1 forms develop from swellings of bacteria, the possibility that a parasite might behave in a similar way cannot be excluded.

On the other hand Dienes's opinion of the bacterial nature of the L 1 component cannot be disproved either. However, we know yet too little about the normal developmental cycle of bacteria to be able to decide whether the L 1 form is an independent entity or whether it may be a normal stage through which bacteria have to pass from time to time or whether it may represent a ‘loss-mutant’ which some bacteria might produce under not yet known conditions. If in the future the bacterial nature of the L1 could be convincingly proved we would be faced with the fact that bacteria can assume a form in which they grow as a thin shapeless slime containing nuclear structures arranged as bodies, rings or very finely dispersed particles—not the dumbbell pattern so characteristic for young bacteria of all kinds—and that further very small parts of the material (filterable granules?) are able to reproduce the L1 culture which at least can go on for many years without reverting into the bacterium from which it was derived.

It has been shown that in all cultures of B. proteus and B. coli a large-cell type with two to four ‘chromosomes’ develops first and produces, after a few hours of growth, by sudden subdivision the smallest unit, a generation of small cells, each with one nuclear structure only. This cell type, singly or in filaments, persists until the end of the growing period. On a ‘swarming plate’ of B. proteus a number of these biphasic growing periods may follow each other.

‘Fusion cells’, in which the chromatinic structures have contracted into a longitudinally arranged bar, are formed when young cultures are stored in the cold.

In a cytological investigation of three branching and two non-branching strains grown on Loewenstein medium, it was found that avian tubercle bacilli contain chromatinic material which gives a positive Feulgen reaction and is readily stainable with Giemsa's solution after treatment of the fixed bacteria with hydrochloric acid.

Growing filamentous forms of both ‘bacterial’ and ‘mycelial’ strains from 1 to 2 day old cultures contain variable numbers of irregularly spaced, more or less spherical chromatinic bodies which vary in staining in the same bacillus, some being red, others purple. During the third or fourth day the chromatinic material in the bacteria increases very much until most of it is fused into an almost homogeneous deeply stained column. In the non-branching strains the filamentous forms with high chromatin content soon break up into small mono-or binucleate elements, and the same holds true for the ‘straight’ filamentous forms which are also present in cultures of branching strains. The ‘mycelial’ forms, on the other hand, disintegrate at this time (fourth or fifth day of cultivation), and it is uncertain whether they contribute (by partial fragmentation) to the masses of small mono- or binucleate forms which are the predominant element in old cultures of all the strains investigated.

The chromatinic structures of avian tubercle bacilli have the same staining properties as those of ordinary non-acid-fast bacteria but differ from them in their behaviour during the early development of the bacilli.

From the faeces of a carrier a strain of Salm. paratyphi B was grown repeatedly which—even under conditions most favourable for bacterial motility—was completely non-motile despite its being richly flagellated and optimally Hagglutinable. The strain has in all subcultures, so far, for more than 1 year retained its peculiarity, viz. absence of the motor function of the flagella which morphologically and serologically appears to be normally developed.

This new bacterial variant, the non-motile H form, is considered to be the result of a loss variation which—possibly related to a somatic degradation of the bacilli—affects the genetic factor responsible for the function or the development of the centre for the motility of the flagella.

1. The total reproductive performance of two groups each of twenty-four mice over a period of one year under two different systems of mating has been recorded.

2. In the first system (monogamous pairs) the male was kept continuously with the female; in 78% of cases the females became pregnant again at post-partum oestrus and were thus subjected for the most part to unbroken intensive breeding.

3. In the second system (polygynous groups) several females were kept with one male and were removed to individual cages for the birth and rearing of the litters and were returned to the male again only after the litter had been weaned.

4. Under the first system 1149 young were successfully reared to weaning in one year by the twenty-four females; under the second system 559 young were weaned during the same period.

5. Mortality of breeding females, litter size, weight of young at weaning, the effect of parity, loss of litters and of young between birth and weaning and the sex-ratio of the young weaned were alike for both methods of mating.

6. The interaction of concurrent gestation and lactation upon the length of the gestation period is discussed, and regression lines showing the relation between the number of young suckled, the number of young in the uterus and the length of the gestation period are given.

My best thanks are due to Dr A. S. Parkes, F.R.S., for advice during the course of the work and for help in the preparation of the manuscript. I should also like to thank Dr C. W. Emmens for the statistical analyses and the calculation of the regression lines.

A study was made of factors leading to loss of working time in a local group of 144 women voluntary factory workers. The majority were single women whose interests centred in their families. One-third of these 144 women, owing to disability of some near relative, had home duties which they realized were sufficiently heavy to interfere at times with their factory work; a contributory cause of absenteeism was ill-health, ascribed by many workers to cold and draughty working environment. Examination of the factory records showed more than twice the rate of absenteeism due to certified sickness among women with home ties and responsibilities.

This study was made possible by the willing cooperation of the Factory Management and their Welfare Department and of the women workers concerned.

One object of the investigation was to determine the ideal contributions to warmth comfort in small ‘domestic’ rooms of air heating and radiation. It was soon found that in rooms heated by fires, subjects usually complained of cold backs when the equivalent temperature was in the region of 60–65° F., the accepted standard for buildings heated by convection, and preferred equivalent temperatures above 70° F.

Since large-scale trials, using many observers, were clearly necessary, the reliability of 5 min. test periods was studied; these short periods were proved reliable so long as the subject had previously been in a comfortable room for an hour or so.

It was found necessary, in rooms heated by fires, to treat separately the side of the subject facing the fire and remote from it. The cooler side must be exposed to an equivalent temperature not much less than 65° F., while radiation falling on the warm side is to be regarded as a very desirable, but nonessential, bonus. These conclusions were confirmed by field work in the subjects' own homes.

The eupatheoscope and globe thermometer were modified to enable conditions acting on the two sides of the body to be assessed separately.

The extent to which radiation acting on the front of the body could compensate for a cold back to produce what was called ‘minimum comfort’ was also studied. It was shown that down to back equivalent temperatures of about 56° F. an increase of 2° in front equivalent temperature will compensate for a fall of 1° in back equivalent temperature, but below 56° F. compensation fails.

The physical basis of sensations of stuffiness and freshness were also investigated. Throughout these experiments care was taken to ensure that the subjects were neither too hot nor too cold. In these conditions, only two factors appear to be important. First, the air temperature should be as low as possible. To obtain warmth comfort with a low air temperature some high temperature source of radiation is generally necessary. The peak wave-length of the radiation emitted by the fire is also of great importance, a striking change in the personal sensations occurring, for example, as the wave-length increases from 2 to 3μ. In general, those wavelengths which are absorbed in the outer layers of the skin cause sensations of stuffiness, and those which are not give rise to feelings of freshness. Peaks at 3, 4·1 and 4·7 μ should therefore be avoided in the design of gas and electric fires.

An analysis of the medical condition of 223 entrants to the nursing profession is attempted, with particular reference to 161 such nurses examined in accord with the recommendations of the King Edward's Hospital Fund for London (1943). This is followed by a short-term medical follow-up on these nurses by clinical examination, weight records, and ancillary tests. Of the total number of entrants eight (3·6 %) were rejected on medical grounds, and four (2·5 %) of the 161 were rejected on the findings of the initial examination.

An analysis of the sixty-five (29 %) nurses lost to the profession in their first year of service shows that 70 % had attempted an uncongenial vocation. It is suggested that vocation selection tests should be tried in attempting to lessen this costly drain of recruits. This figure of 29 % is no higher than the peacetime figure found by the Lancet Commission (Athlone Report, 1938).

An analysis of the illnesses of the nursing staff at Westminster Hospital during 3 years from 1 July 1943 to 30 June 1946 is presented, nearly 60 % of the illnesses being accounted for by respiratory tract infection and cutaneous sepsis. It has been shown that illness of more than 50 days in duration accounts for only 5 % of attacks of illness, but practically 30 % of the time lost through illness. It is suggested that such illness should be differentiated in analyses, from illnesses of shorter duration. A comparison of illnesses in staff nurses and student nurses follows; the figures suggest a lower morbidity rate in staff nurses, but the number of staff nurses is so small that the author cannot state that this has been demonstrated.

A comparison table between previous illness surveys and the present figures is presented which demonstrates a decreasing number of attacks of illness per nurse over the last 20 years in this country, probably due to better basic conditions of life.

A similar but international comparison applied to respiratory tract infection and cutaneous sepsis demonstrates that the former accounts for about 40 % of all the attacks of illness in this country and internationally. The previous figures for Great Britain, however, are exceptional in showing a much higher incidence of sepsis than elsewhere; this has not been substantiated by the present survey.

Figures for the amount of time lost per year through sepsis, tonsillitis and catarrhal disease are compared with those of Branson (1933) of 20 years ago, and perhaps illustrate the beneficial effect of surgery in cutaneous sepsis, and of sulphonamides in tonsillitis, as against the negligible therapeutic advances in catarrhal disease. The amount of tonsillitis sustained by nurses in the children's ward is shown as being out of proportion to the number of nurses employed.

Finally suggestions are made for promoting the health of nurses, which include: (i) the provision of a ‘welfare officer’ in the nurses' home; (ii) illness allowance proposals; (iii) remarks on the technique of ‘reporting sick’; (iv) staffing children's ward with senior nurses only.

Although the composition of blood is assumed to be constant within narrow limits, fluctuations in concentration of its constituents have been found by many observers over the period of a day or longer. Shaw (1927), Jores (1934) and others describe daily fluctuations in the white corpuscles, and Sabin et al. (1925) found similar changes in the blood platelets.

Attack by the cercariae of Schistosoma haematobium, S. mansoni and S. japonicum causes in man debilitating diseases which in certain countries are widespread. Infection is mainly through the skin, though it can occur through drinking water containing the parasites. It has been shown by Sproule (1939) that freshly liberated vigorous cercariae of S. haematobium and S. mansoni are killed in 30 min. by superchlorination to the extent of one dose beyond that indicated in the Horrocks test. This of course does not deal with skin infection, and though bathing in fresh water may be avoided and water drawn off may possibly be stored till all cercariae are dead, yet it is obviously impossible entirely to avoid contact with natural waters. In U.S.A. and Canada dermatitis is caused at many otherwise desirable lacustrine bathing beaches by cercariae liberated from Stagnicola emarginata and other snails which live in shallow water on sandy bottoms (Cort, 1928; Brackett, 1941). The final hosts are apparently water birds and in man these cercariae tunnel in the epithelial layer of the skin and soon disintegrate. No dangerous disease is caused, but there is much discomfort, especially among children who naturally keep to the shallow water. Penetration takes place largely as the water film dries and oiling the skin is no preventive. McMullen (1941) has given an account of attempts to eliminate the parasites by poisoning the snail hosts with copper sulphate or a sulphate carbonate mixture. A temporary success can be achieved at considerable cost.

A statistical study has been made of the records of respiratory infection in a portion of Wensleydale, Yorkshire, over the period 1933–46, which included three major English influenza A epidemics and one B epidemic.

Each of these epidemics is recognizable in the Yorkshire records. When the incidence in the eight groups of villages comprising the district is compared there is a significant negative correlation between incidence in 1933 and 1936–7, which is taken as indicating the persistence of group immunity following an influenza A epidemic for 4 years.

There was a significant positive correlation between the incidence of the 1943–4 (A) and 1945–6 (B) epidemics.

1. The occurrence under natural conditions of foot-and-mouth disease in the hedgehog, Erinaceus europaeus, is reported in connexion with outbreaks of the disease among farm stock in Norfolk during the summer of 1946.

2. Foot-and-mouth disease may be fatal in the hedgehog which decreases the chance of finding affected animals and of revealing the existence of the disease.

3. In this series of outbreaks it seemed probable that affected hedgehogs were responsible in some instances for spreading the disease to cattle and the possible role of the hedgehog in the epidemiology of the disease is discussed.

1. A brief introduction to the Conglutination Phenomenon and to the Conglutinating Complement Absorption Test is given.

2. The reasons are stated why we think that further investigations into this phenomenon are desirable.

3. An account is given of the publications on the mechanism of the reaction, the hypotheses regarding it and its applications since the original observations of Ehrlich & Sachs in 1902.

1. A brief introduction has been given to the conglutination reaction.

2. The technique used by us for carrying out the conglutinating complement absorption test has been described in detail and compared with that used for the haemolytic complement fixation test.

1. Observations on the sera of ponies, taken at frequent intervals for 321 days after oral administration of P. mallei, are described.

2. It was found that the conglutinating complement absorption test was more sensitive than the haemolytic complement fixation test as a means of diagnosis. It detected the antibodies earlier in the course of the disease and demonstrated their presence over a longer period of time.

3. The possibility of another practical use of this reaction as an adjunct to the allergic test is considered. Ten days after an intradermo-palpebral test a pony, which had been previously sensitized and whose serum antibody titre at that time was below 10, developed a serum titre of over 160 as demonstrated by the conglutinating complement absorption test. Under similar circumstances 11 unsensitized ponies developed no detectable serum antibodies.

Section I

A standard bacteriological test for molluscan shellfish should fulfil certain requirements stated: briefly, the test should show the degree of pollution, be accurate and rapid, and self-sufficient, not requiring subsequent confirmation. Review of the subject leads to recommendations, first, to overcome the technical difficulties of preparing samples for testing; secondly, on the nature of the test. In preparation: external shell sterilization can usually be omitted, shell water should be discarded and replaced by sterile water to make a total volume three times that of the body tissues. Pooling of individual shellfish into one sample is acceptable in routine examinations. In the test: a solid medium is preferable to a liquid medium, giving more accurate results, and review of existing tests leads to the conclusion that the use of roll tubes of MacConkey agar incubated at 44° should meet the requirements of a standard test.

Section II

A modification was found necessary in the MacConkey agar: a mixture of 2 % gelatin and 5 % agar is used instead of the normal 2 % agar. Mechanical rolling devices for tubes are described and figured.

Among other critical experiments, 1000 roll-tube colonies grown at 44° from shellfish included 969 with + + − − ‘IMViC’ reactions and 979 acid and gas producers at 44°. The coefficient of variation among replicate tests of samples of shellfish and water in roll tubes was not seriously greater than that for colony counts in Petri dishes at 37° with ordinary MacConkey agar.

Colonies in roll tubes incubated at 44° can be counted as conveniently and accurately as those on Petri dishes, and, in general it is concluded that the new method is more satisfactory for estimation of faecal coli than other methods at present in use.

Section III

Directions are given for the preparation of shellfish and inoculation into roll cultures, both for individual and for pooled examination, and the method of determining results is described.

The interpretation of results is discussed, and it is suggested that shellfish which in four out of five samples from the same source are free from faecal coli in 1 ml. quantities of body tissue should be regarded as satisfactory for food. The presence of more than two or three faecal coli per ml. of body tissue in any one sample calls for appropriate action according to the number present.