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Report of the Medical Officer of Health.
121
bacteria to invade the tissues shortly before death. Moreover, these organisms were more plentiful
in milk in summer than in winter, and this increase should have been accompanied by a corresponding
heavier summer mortality, yet Chart I. shows that this expectation was not borne out.
Again, if the milk sediment was the only lethal agent, one would expect that if one animal died,
its companion, injected with an equal quantity of the emulsified sediment, would also die. Yet the
number of samples associated with the death of one animal is more than double that of those associated
with the death of both, so that we must conclude that the milk sediment injected is not the only factor
involved, but that it is often only a contributory cause of the mortality.
The sediment contains cells from the milk and a very large number of bacteria, some pathogenic
to guinea-pigs, some non-pathogenic ; and we know from the results of the injection of dead cultures of
organisms (vaccines) into man and animals that the bodies of bacteria contain constituents which may
produce a great disturbance of health, accompanied by a lowered resistance to infection in general.
Clinical evidence suggests that in consequence of disturbed conditions of general health, or of local
disturbance, as in injury to the intestines, organisms normally present in the intestine may migrate
therefrom and invade the tissues, producing severe or possibly fatal results.
A careful review of the whole evidence suggests that a large part of the mortality amongst
guinea-pigs inoculated with the sediment of milk is occasioned in a similar way, the milk injected so
lowering the general health that a disease which is latent or chronic is able to progress to a fatal issue,
or bacilli normally present in the intestine are enabled to escape into the circulation and cause death.
In a paper which has recently appeared some experiments are described in which white mice
were fed with cultures of various bacilli of the food-poisoning group—to which group the B. aertryck
belongs. The observers, Zwick and Weichel (w) obtained results which led them to a similar conclusion.
Some of their fed mice survived and were found to be execreting the bacillus with which they had been
fed in their faeces for many days afterwards, although they appeared to be perfectly healthy. These
animals when injected subcutaneously with a sterile emulsion of sausage meat died and the bacillus
was isolated from their organs. The authors explain this by assuming that the inoculation lowered
the animal's general health and its natural power of preventing the migration of the bacilli from the
intestine, so that these bacilli invaded the organs and caused death.
The presence of the faecal or lactose fermenting organisms in the organs of the dead guinea-pigs
seems, on the whole evidence, to be explicable only on a similar hypothesis. The toxic sediment lowers
the animal's resistance so that the normal intestinal organisms of the guinea-pig rapidly leave the
intestine, invade the organs and cause death. Thus, the source of these faecal organisms found postmortem
is not in all cases necessarily the dung of the cow-yard, but often probably the guinea-pig's
intestine.
Summary and conclusions.
The object of the investigation was to determine the cause of the "non-tubercular mortality"
amongst guinea-pigs and any bearing this might have on the general question of the purity of London
milk. By "non-tubercular mortality" is meant the mortality from causes other than tuberculosis
amongst guinea-pigs injected with the sediment from samples of milk.
1. A part of this "non-tubercular mortality" was due to infectious diseases which the animals
were incubating at the time they were inoculated with the milk sediments, or with which they became
infected during the month they were allowed to survive prior to examination for tuberculosis. This
was notably the case during November and December, 1909.
2. Infection by bacilli identical with those derived from the faeces of cows and other animals
contained in the milk inoculated is responsible for a certain amount of the "non-tubercular mortality,"
this amount being impossible to determine accurately.
3. The greater part of the mortality, however, appears to be occasioned by a combination of
factors. A disturbance to the animal's economy is occasioned by the considerable dose of bacterial
protein in the sediment, quite apart from the capacity of such bacteria to survive in the tissues. This
may so lower the resistance of the animal that it succumbs either to an aggravation of an existing but
hitherto indolent infection—e.g., pseudo-tubercle—or to the invasion of the organism by bacilli present
in its intestine.
4. No evidence was obtained of the presence in the milk of bacilli causing common diseases in
man, such as typhoid fever, diphtheria, dysentery, or "food-poisoning."
(w) Zwick and Weichel ; Arb. aus. d. Kaiserlich. Ges. Bd. 32, 1910.
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