The two generally recognized divisions of the country are the Delta (Lower Egypt), extending from the Mediterranean littoral to Cairo; and Upper Egypt, the narrow strip of alluvial soil in the Nile Valley from Cairo to Wadi Halfa. The valley of the Nile is a rift valley formed by the subsidence of a narrow belt in the neighbourhood of a line of fracture on the earth's surface; from Cairo to Aswân town its length is 880 kilometres (547 miles), and its width varies from 3 to 21 kilometres (2 to 13 miles). The province of the Faiyûm is a depression which is irrigated from the Nile by the Bahr Yûsef Canal, one of the old natural drainage channels of the valley.

In the preceding pages, an analysis has been made of the correlation coefficients found between the number of fatal cases from bronchitis, pneumonia and respiratory diseases, or the two summed together, in children under five years of age in London, Glasgow, Edinburgh, Aberdeen and Dundee, and the meteorological factors, mean and mean minimum temperature, mean relative humidity and mean rainfall, for a period of from 40 to 50 years; and between the death-rates from bronchitis, pneumonia and respiratory diseases amongst children at the same period of life in the registration counties of England and Wales in the decennia, 1901–10 and 1891–1900, and their mean annual temperature and mean annual rainfall and it seems warrantable to draw the following conclusions.

1. The meteorological factor, amongst those investigated, that seems to exercise the greatest influence in predisposing to an increased mortality from, and presumably an increased incidence of, bronchitis in children in the cities, is the prevailing temperature. In accordance with the average duration of the disease, the mortality is most intimately related to the mean temperature of the preceding week and is, on the average, as closely related to the temperature of two weeks before as it is to that of the corresponding week. The relationship is inverse, the lower the mean temperature the greater the fatality from bronchitis. As suggested by Dr Leonard Hill, the cold weather probably compels children to remain indoors in stuffy, overheated rooms where infection is intensified and health weakened by heat stagnation, a lowered metabolism and want of sunlight.

2. While there is a suggestion from some of the correlation coefficients found, that pneumonia in children may have some inverse relationship to mean temperature this association is not shown in the monthly or weekly data generally.

3. There is a definite inverse relationship between the mortality from the respiratory diseases, or bronchitis and pneumonia summed together, and the mean temperature; and, as occurs with bronchitis, the relationship to the mean temperature of the preceding week is closer than to that of the corresponding week.

4. The mortalities from bronchitis, pneumonia and respiratory diseases (bronchitis and pneumonia summed together), in children under five years in the registration counties of England and Wales, are inversely associated with the mean annual temperature in the corresponding counties. This association still persists after allowance is made for the proportion of each county which is urban, a proportion which has been taken as a rough index of industrial conditions therein.

5. The mortalities from bronchitis and pneumonia in children in the cities examined and in the registration counties are not influenced in any consistent manner or degree by the amount of rainfall.

6. While the coefficients of correlation between the corrected monthly deaths from bronchitis and respiratory diseases, respectively, and the corresponding mean monthly humidity in Glasgow seem to suggest the existence of a significant direct association between these variables, viz. the moister the atmosphere, the higher the death-rate from bronchitis; such a relationship is not definitely indicated in the coefficients found for the other cities. The magnitude of the coefficients for Glasgow is apparently determined, in some degree, by the periodicity in the mortality figures. It is probable, however, that the periodicity is not wholly responsible for the correlation found as the correlation coefficients between the mean temperature and the deviations in the same monthly data from the five-yearly moving average—the method adopted to eliminate the effect of the periodicity—are not very different from those found by using the actual figures. There would appear to be some evidence for the view that a high relative humidity, when associated with a low temperature, has some influence in predisposing to an increased mortality from the respiratory diseases.

The object of the present investigation was to determine the relation between the variations in hair and eye colours and variations of weight and stature; so that one might know what allowances, if any, would be necessary to make for variations of the proportion of children in different classes of hair and eye colour in different age groups and in the two sexes in the different schools under investigation with respect to the factors influencing bodily growth and nutrition. Incidentally, the analysis might reveal racial differentiation if such were present in this population.

In a study of the influence of environmental and other conditions on the growth and nutrition of the children of the poorer classes in the city of Glasgow, it seemed desirable to determine how far a homogeneous stock was being dealt with since there was some danger that racial variations might modify the results of the investigation.

We may summarise our results, including those recorded in our two recent reports (Topley and Ayrton, 1924 b and c) under the following headings.

(1) The antigenic structure of B. aertrycke (Mutton).

(a) B. aertrycke (Mutton) undergoes natural dissociation into two sharply distinguished varieties, one containing that antigenic constituent which is characteristic of this bacterial species or variety, the other that antigenic constituent which B. aertrycke (Mutton) shares with the bacterial group to which it belongs. We have obtained no evidence that both the type and group antigen may be fully developed in one and the same bacillus. In these respects our results confirm entirely those recorded by Andrewes (1922).

(b) Both the type and the group varieties of this organism, when grown for more than 16 hours at 22° C., or for that length of time at 37° C., tend to undergo an antigenic alteration such that they become agglutinable with an entirely different type of antibody, to which they did not previously respond. The antigen developed as a result of this alteration would seem to be the same for the type and the group varieties. Since plating from such altered cultures gives colonies of the usual type or group variety, it would seem probable that the altered bacilli are dead, dying or senescent organisms.

(c) Although type or group cultures readily give rise to individuals of the alternative antigenic variety in ordinary laboratory media, yet this change is neither so rapid nor so unpredictable in its occurrence that it is impossible to determine the nature of any given colony, or to obtain a culture of the serological variety required.

(d) There is some evidence that type variants arise in group cultures more readily than do group variants in type cultures.

(2) The relations between the presence of type or group antigen and other biological attributes of B. aertrycke.

(a) Roughness and smoothness vary independently of the presence of group or type antigen. Rough forms may react as group or type.

(b) There is no difference between the virulence of the type and group varieties of B. aertrycke. While the virulence of all smooth strains is high, the virulence of all rough strains is low.

(c) There is some evidence that group strains of B. aertrycke give rise more readily to faecal excretion than do type strains, but the difference is not great. Rough strains appear, in this as in other respects, to be ill fitted for a parasitic existence, and do not give rise to persistent faecal excretion.

(d) There is a well-marked tendency for group strains, which have gained access to the tissues, to give place to the type variety. The longer the sojourn in the tissues, the more complete is this replacement. Type strains, under similar conditions, do not tend to be replaced by group strains.

There is a similar, but less marked, tendency for group strains to be replaced by type strains in the intestinal canal.

(3) The excretion of B. aertrycke in the faeces, after administration by the mouth, and its relation to other phenomena of infection.

(a) The excretion of B. aertrycke in the faeces, after administration per os, may be continuous or intermittent, or may not occur in a sufficient degree to be detected by the technique employed.

(b) The faecal excretion, in those mice which succumb to infection, is no more regular in its course than in those mice which survive. It is a frequent occurrence for mice to die with typical lesions of enteric infection, without ever having excreted B. aertrycke in detectable amounts.

(4) The condition of mice which have survived the oral administration of B. aertrycke.

(a) A high proportion of mice, which have survived for 42 days after the oral administration of B. aertrycke, yield cultures of this organism from their spleens when examined post-mortem. In many series of experiments the proportion of survivors showing such positive spleen cultures has exceeded 50 per cent.

(b) The strains of B. aertrycke isolated from the spleens of such survivors appear to be possessed of the normal degree of virulence.

(c) The presence of agglutinins in the blood serum can be demonstrated in only a very small proportion of such surviving mice.

(5) The relation of dosage to the phenomena studied.

(a) With a single dose, there is a definite relation between the number of viable B. aertrycke administered and the frequency of the phenomena indicating infection. The larger the dose the higher is the mortality rate, the more frequent and persistent is the faecal excretion, and the higher is the percentage of the survivors which harbour B. aertrycke in their tissues.

As the dose decreases there is, at first, a rapid fall in the frequency of these various phenomena, but when the dose falls below a certain limit further decreases produce relatively little effect, over the range of doses studied.

(b) Repeated administration of small doses of B. aertrycke results in a high frequency of persistent faecal excretion.

In conclusion we should wish to express our thanks to Miss E. R. Lewis, for her assistance during a large part of the investigations recorded above.

In previous reports (Topley and Ayrton, 1924 a, b and c) we have recorded the results obtained by feeding mice on cultures of B. aertrycke, and studying the subsequent excretion of that organism in the faeces. The present report deals with the application of the same technique to the study of an experimental epidemic of mouse-typhoid.