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In the B Class, comprising 66 houses invaded by multiple cases, the percentage of dwellings
with fixed brick ashpits, half paved or dirty yards or many flies was notably higher than among the
392 houses where single cases of diarrhoea occurred. Flies were noted under the three heads,
"Many," "Few," or "None": no numerical definition was attempted for these expressions, and
no definition was attempted of the conditions of a yard which would justify the description " dirty."
In these two particulars any bias in the mind of the observer would, therefore, have inevitably
affected the reliability of the records. It is accordingly important to note that bias could not have
existed when the records were made, since the comparison of the sanitary surroundings of multiple
and single cases was not thought of until the end of the year.
When the incidence of diarrhoea on a house is limited to one case, there is frequently an equal
chance that the patient may have acquired the disease outside the premises or district in which
he lives. When the incidence is multiple, the chances are against external infection and in favour
of a common cause within the premises where the patients attacked reside together under the
same roof. Flies and the brick ashpits in which they breed have been suggested as potential
sources of infection when diarrhoea is prevalent. The fact that the proportion of houses containing
many flies was five times as great, and the proportion with fixed brick ashpits twice as great in
the B Class, may therefore be legitimately regarded as significant.
The four last conditions named in the Table need not be discussed, as the figures do not
suggest that they exert any influence in the production of multiple infections.

The immunity of children taking no food except their mother's milk is shown by the small
number of the breast fed among the infants who were attacked. And this immunity becomes more
striking when account is taken of the fact that the number of breast fed babies is very large, and
that more than 65 percent, of the infants who are born in Kensington and who survive are still at
the breast between the ages of 5 and 7 months, and receiving no other food. Of the artificially
fed in the normal population under the age of 7 months less than one-sixth are fed with condensed'
milk. Of the artificially fed of the same age among those who suffered from diarrhoea, more than
one-fourth had been fed with condensed milk, which has in a number of independent observations
in different districts been found to increase the liability of infants to attack.