View report page

116
Annual Report of the London County Council, 1910.
Cultural methods.—Cultures were taken with the usual precautions against contamination, from
the heart-blood, liver, spleen, the local lesion at the site of inoculation and sometimes from the
mesenteric glands. Broth tubes and MacConkey lactose-bile-salt-neutral-red-agar plates were inoculated
from each specimen and incubated at 37 deg. C. If colonies appeared on the plates, cultures were
made for identification, one or more being used according to circumstances. If the plates when
examined next morning showed no growth, the broth cultures were inoculated on MacConkey plates
and then incubated. In the earlier part of the investigation, whenever these second plates showed no
growth, the broths were inoculated on ordinary agar plates. In such cases it was found that cocci
sometimes developed. Guinea-pigs are known to be very resistant to cocci, and the pathogenicity
test confirmed this view for the strains of cocci isolated, so that these were considered to be accidental
contaminations having no relation to the cause of death. Subsequently, therefore, MacConkey plates
alone were used.
Frequently both plates and broth showed no growth—in one series of 191 examinations this
occurred 48 times ( = 25 per cent.). This suggested the possibility of the existence of toxins, or
anaerobes in the milk as possible causes of death. The former possiblity is considered at p. 118. In
order to see if anaerobes were present 14 tubes that showed no growth after incubation aerobically
were incubated anaerobically. No growth occurred in any of them, and no further anaerobic cultures
were made.
The identification tests used were largely those elaborated by MacConkey in his various papers
on intestinal organisms, for it became apparent early in the investigation that the predominating
organisms isolated grew well on MacConkey's medium and were probably of intestinal origin. The media
used in all cases were solutions in peptone water of lactose, mannite, dulcite, saccharose adonite, and
inulin. Other carbohydrates as glucose, galactose, dextrin, maltose, sorbite, raffinose and arabinose
were made use of in special cases. The reaction in Litmus milk was observed up to fifteen days; indol
production was tested for after five days' incubation at 37 deg. C. by Ehrlich's test; and for the
determination of motility six to eight hour broth cultures were used. Cultures on gelatin were made,
and examined a month or more later, for the presence of liquefaction.
Main lines of enquiry.
For the sake of clearness, the main lines of enquiry are set forth here in order:—
(i.) The possible occurence in the milk samples of bacilli pathogenic to man.
(ii.) Identification of organisms isolated from the guinea-pigs on post-mortem examination.
(iii.) Consideration of the number of organisms injected with the milk deposit.
(iv.) The contribution of naturally occuring dieases amongst guinea-pigs to the observed
mortality.
(v.) Experiments with sour milk, injected (1) untreated, (2) after filtration, (3) after being
boiled.
(vi.) Attempts to correlate (1) the period of year and temperature, (2) the number of lactose-
fermenting organisms present in the milk samples, with the daily mortality and with
the death-rate recorded in relation to the date of inoculation.
(vii.) Results of inoculation of milk samples from single cows noted as "possibly diseased"
on veterinary inspection.
Search for occurrence in milk samples of bacilli pathogenic to man.—As this was a point of importance
from the practical public health aspect, attention was directed throughout the investigation to the
possible presence of such pathogenic organisms. The literature dealing with their occurrence in milk
may first be briefly reviewed.
The bacilli of typhoid fever in milk.—There are in the literature (j) more than 300 cases (many
of them in Great Britain) in which the epidemiological evidence showed that certain milk supplies had
almost undoubtedly been responsible for typhoid epidemics. I have made a search through the literature,
but have found no case in which the B. typhosus was discovered in a milk supply in a routine
examination, that is, without a previous suspicion that the given sample was infected. Reynolds, in
1902, stated that in eight years special search for this bacillus in Chicago milks had revealed it in three
instances, but then only where local epidemics had directed suspicion to certain milk supplies. In the
literature referring to the many epidemics, I have found only three instances (k) in which the typhoid
bacillus was recovered from milk.
In this investigation the methods were designed to yield as comprehensive results as possible,
and the search for bacilli pathogenic to man, except in the case of the Gaertner group, was not specifically
made. Yet it is interesting to find that no suggestion of the presence of the B. typhosus in the 2,520
milk samples received during the period under review has arisen either from an investigation of the
effects of the deposits when injected into guinea-pigs, or of the results of direct inoculation of the milk
on plates, in 111 instances in which this was done. Similar negative findings as regards London milks
are recorded by Klein (l), and Hewlett (m).
(j) Swithinbank and Newman; Bacteriology of milk, 1903, p. 316. Bulletin, 56, Hygienic Laboratory, U.S.A., 1909,
p. 29. Sommerfeld ; Milchkunde, Berlin, 1909, p. 1901. Schüder; Zeitschr. f. Hyg. u. Inf. Kr. Bd. 38, p. 343.
(k) V. C. Vaughan; Ann. Rep. State Board of Health, Michigan, 1891, p. 216. Shoemaker; Journ. Amer. Med.
Ass., 1907, p. 1748. Conradi; Centr. bl. f. Bakt. Abt. Bd. 40, p. 31.
(l) Klein; Journ of Hygiene, 1901, p. 85.
(m) Hewlett and Barton; Journ. of Hygiene, 1907, p. 27.