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8
June 7th a.m.—Separated.
p.m.—" A "—Cases occurred a few days later among " A's " customers.
,, 8th a.m.—Separated.
p.m.—One vendor, none of whose customers were attacked,
and " B " and " C "—Cases occurred a few days later among their customers.
„ 9th a.m.—No record.
p.m.—" D "—Cases occurred a few days later among his customers.
,, 10th a.m.—No record.
p.m.—" D " and " E "—Cases occurred a few days later among their customers.
,, 11th a.m.—No record.
p.m.—Two vendors, none of whose customers were attacked.
,, 12th a.m.—No record.
p.m.—One vendor, none of whose customers were attacked.
,, 13th a.m.—No record.
p.m.—One vendor, none of whose customers wore attacked.
and " O "—Cases occurred a few days later among his customers.
,, 14th a.m.—" H," " I," " J "—Cases occurred a few days later among their customers,
p.m.—" K," " D "—Cases occurred a few days later among their customers.
,, 15th a.m.—Separated.
p.m.—" K"—Cases occurred a few days later among his customers.
,, 16th a.m.— No record.
p.m.—" B," who had already had this milk on the 8th.
and "M"—No outbreak occurred among his customers.
„ 17th a.m.—Separated.
p.m.—" £)," who had already had this milk on the 9th, 10th and 14th.
,, 18th a.m.—No record.
p.m.—No record.
,, 19th —None went out.
If it be assumed, and the reasons for making tbis assumption will be given later (see below),
that the date on which infected milk was distributed to F's customers was subsequent to June 6th, it
will be seen from the above record that—
(a) The distribution on June 7th, 8th, 9th and 10th of the milk from farm X was associated
with the development of scarlet fever.
(b) No cases of scarlet fever are known to have occurred among persons supplied on June
J 1th and 12th with milk from farm X. (It should be mentioned, however, that on
June 12th milk from farm X was sent to a London station, 15 gallons being consigned
to a particular vendor. This vendor's customers were not attacked, but cases
of scarlet fever developed on June 14th among consumers of milk obtained from the
company and dispatched on June 13th from the London station in question, and it is,
of course, possible that the persons attacked had drunk milk derived from farm X.)
(c) On June 13th and onwards distribution of the milk was again associated with development
of scarlet fever.
In other words, it would appear that the milk distributed from farm X was infective on June 7th,
8th, 9th and 10th, non-infective on June 11th, and probably on the 12th, and became infective again
on June 13th and onwards.
If this assumption be made two points require explanation :—
(1; The apparent escape of persons consuming milk obtained from vendors who received
chance consignments of milk from farm X on one or other of the days 11th, 12th and 13th.
In explanation of this the most likely hypothesis is that the milk sent from farm X to the
depot included the milk of one or more infective cows on June 7th-10th, and again on June 13th and
onwards, but that it did not include such milk on June llth-12th. Alternatively it might be
suggested that on particular occasions only certain churns from farm X contained infective milk. It
■will be remembered that farm X comprised two separate farmsteads, X1 and X2. The milk from
these might or might not be mixed, according to the amount of supply from each farmstead in
relation to the size of the churns. No record as to whether such admixture had occurred was available.
There were usually two or three churns of milk dispatched from farm X to the depot each
morning and evening, and rather less in the evening than in the morning. Moreover, a considerable
amount of milk was pasteurised at the depot each morning. If it be assumed that on
the particular days, viz., June 11th and 12th, and partially on the 13th also (on the 13th—see
Table—some milk was infective) some of the evening milk was also pasteurised, though of this
we have no evidence, and that on those days only certain churns contained infective (as distinguished
from non-infective) milk from farm X, and the milk in those churns happened to be
completely sterilised by the pasteurising process, explanation of the observed phenomena would be
forthcoming. The odds against such a combination of chance occurrences are, of course, considerable.
(2) In the case of supplies F and A already referred to, and of M (see above, page 6) and N
and P supplies not yet mentioned, the recorded facts do not fully explain the observed phenomena.
F is said to have received milk from farm X only on the 6th, but it seems, judging by the dates
of cases occurring on his round, that the mischief among his customers was of later date. As has
already been noted, F received mixed "pasteurised" milk (possibly, therefore, unsterilised X milk)
on the 9th, 10th and 11th, and it may be that some of this mixed milk caused the mischief. Again
A is said to have received milk from farm X only on the 7th, when he had two churns of it. A
also received mixed " pasteurised " milk, however, on a number of occasions, and having in view the
extent to which his customers were involved, question arises as to whether some of this mixed milk
was derived from farm X. Again, A's customers were in large part well-to-do people, who might
be presumed to consume separately purchased cream, and some of this cream may have been derived
from farm X. The escape of M's customers constitutes another difficulty. He may, however, have
had only a very small amount of milk.
Among the customers of N and P, vendors not included in Chart I., who were supplied by the
dairy company from the implicated depot, a few cases of scarlet fever are known to have occurred,