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B's would contain a trace of A's and of C's; C's a trace of B's and of D's, and so on. In the main,
however, but little admixture of milk seemed to occur during the cooling process. No cleansing of
the vessels used or of the refrigerator took place between each consignment of milk. When the
milk from one farm was insufficient to fill the receiver, there was often some addition of milk from
another farm, in order to ensure full vessels.
Pasteurising.-As a rule, only the morning milk (or rather part of it) underwent this process, there
being more time available for it in the morning than in the evening. It may be mentioned that some milk
vendors refuse to accept pasteurised milk on account of its peculiar taste. During the "pasteurising"
process the contents of the churns as they came into the depot were poured into a large receiver, being
mixed whenever necessary to secure a full vessel. From the receiver the milk was pumped into a
reservoir, delivering into a pasteurising cylinder, which was kept at a temperature of 150° to 160° F.
The milk entered at the bottom of the cylinder and the process lasted while the milk flowed from the
bottom to the top and out; this being a continuous flow the duration of exposure to the high temperature
of any given specimen of milk could not be exactly stated, but it was variously estimated at
from 5 to 15 minutes. In any case, the process of sterilisation could not be assumed to be a complete
one. From the steriliser the milk passed over the refrigerator and was delivered into the churns. This
process of pasteurisation, being continuous, involved mixing of milks as a matter of course. The
consignments to vendors after pasteurisation could not be checked as from particular farms, and the
only record of distribution kept was that pasteurised milk had been sent to the consignees. It will
be obvious from this description that we had to reckon with the possibility that some even of the
so-called pasteurised milk might be infective.
The records supplied to us as to distribution of milk from the farms were therefore only to be
trusted subject to considerable limitations. It was obvious that they did not completely account for
all the milk from each farm. Milk not accounted for might be included in the pasteurised milk ; it
might, again, have been separated, the cream being sold, and, again, it might have been made into
cheese, while some skim milk was used for feeding pigs ; finally, the milk might have been dispatched
in the raw state, at any rate in small quantities, to vendors not recorded as having received it, being
mixed with other milk as above indicated, or used to make up a churn of milk in the main supplied by
some other farmer which fell somewhat short of the required measure.
Attention must now be directed to Chart I., showing the sources of supply to vendors in
London and Surrey whose customers were attacked by scarlet fever.
In this table letters A, B, C, etc., which indicate the several vendors, are placed at the heads
of a series of vertical columns. In our original table prepared on June 20th, we took the names of
vendors more or less at random, but in the present table the vendors are arranged (in the light of
knowledge since obtained) in the order of development of scarlet fever in the several districts supplied
by them. Our original table did not include vendors J, K, and L, of whose implication in the
outbreak we had no certain knowledge on June 20th. Moreover, we included a vendor M, who was
then suspected to be implicated, but whose customers it has since transpired did not experience any
unusual incidence of disease. In this table zigzag lines indicate the dates of occurrence of first
symptoms in the earliest cases, so far as they could be ascertained by careful enquiry in the several
districts, and the table shows, broadly speaking, that milk from farm X was distributed shortly
before the outbreak of scarlet fever in each of the implicated districts.
We desire to call special attention to the case of vendor A. The information we received in
the first instance was to the effect that the earliest cases among this vendor's customers were not notified
until June 18th. Further enquiry, however, was made into the matter, and the Medical Officer of
Health of the district concerned wrote as follows: " The doctor who notified nearly all the cases, on
the 18th, says that he had several cases of sore throat during the week previous, not followed by
rash and not notified. I have also notes of three similar cases where other persons in the house
subsequently developed scarlet fever with rash." The records of milk distributed show that vendor A
received two churns of milk sent from farm X on June 7th ; possibly the anomalous character of the
early cases among his customers may justify the assumption that the milk possessed on that day a
modified infective property as compared with that derived from the same source at a later date.
At the time when we constructed our original table we were led to the conclusion that only three
farms came under suspicion, but upon further consideration we added a fourth farm to this group.
It was clear that the milk from the farm or farms at fault must have been distributed either raw or
after "pasteurisation " in every one of the affected districts to account for the outbreak. Apart from
any question as to human illness at any of the 31 farms supplying the depot, it may be stated that,
excepting X, Y, Z and another farm, which may be designated as W, no one farm's milk had been
sent to more than four of the affected vendors in June.
The cases of Z, Y, W and X may be discussed in some detail. Taking the records as giving
approximately a correct account of the distribution of the milk, it will be seen at once (vide Chart)
that the milk of farm Z cannot have caused the scarlet fever. This milk was not sent to vendors
B and C prior to June 13th, and did not go to E until the 15th, a date certainly subsequent to the
outbreak of the epidemic in E's district. It did not go to F at, all, and it was not supplied to H
between the 10th and 17th (H's cases were, as far as could be judged, probably infected about the
14th). Again, it was not supplied to G or A, while D had it only once on the 13th. Furthermore,
most of Z's milk went to I, and yet I had only some 20 cases, while A, who had a great many more
cases, did not, as already noted, receive Z's milk at all.
Taking next the milk of farm Y. The date of consignment to C, June 15th, was here
too late to account for the scarlet fever on his round; so also was the date (16th) of consignment to
H. I had none of Y's milk, nor had G. On farms Y and Z it will be remembered there were cases
of illness among children (see p. 5), which enquiry had shown to be cases of measles.
The milk from farm W was sent to all the vendors known on June 20th to be implicated save
G and A, but its dispatch on the 6th and on the 18th to I would not explain the phenomena observed