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22
Annual Report of the London County Council, 1914.
from the difficulties experienced in applying their doctrines to actual cases investigated, by having
recourse to new hypotheses resting upon a bacteriological basis, such as that of conveyance by flies,
or again, after failing, as a rule, to find any evidence of direct infection from the sick, by the appeal
made rather more than ten years ago by the school of Koch to the healthy carrier.
There results from scrutiny of the changing fashions of aetiology during the last fifty years a
tendency to lay stress on one or other of two types of theory. There is the theory of Koch that the
bacillus causes the disease and that its habitat is the human body; and acceptance of this apparently
implies need for assuming that the bacilli of healthy carriers vary in their infectivity and that they
can by some change which is not understood, from time to time become effective, and then cause mischief
either by direct transference from human excreta by means of fingers, etc., or by dispersion through
the medium of milk and shellfish; it is especially noteworthy that during the last five or six years the
intermediation of infected food materials has been increasingly appealed to by Koch's followers. On
the other hand, there is the theory that the bacillus is produced by the diseased conditions set up in
typhoid fever, which so influence certain saprophytic germs commonly present in the human intestine,
as to cause their mutation into bacillus typhosus or forms closely allied thereto. According to this
theory the causa causans of typhoid fever remains still to be discovered, but its main means of obtaining
access to the human body are again, generally speaking, those same food materials to which the school
of Koch now attaches such great importance. The controversy from a practical preventive point
of view may then be said to turn largely upon the question, do the food materials owe their infective
properties to their becoming contaminated by typhoid bacilli, or by the as yet unknown causa causans
of typhoid fever ? The great importance of correctly answering this question will be realised on examination
of two particular cases in point. In Belfast it is claimed that typhoid prevalence has been greatly
reduced by preventing consumption of sewage-contaminated cockles; in south-west Germany it is
claimed that a similar reduction has been accomplished by dealing stringently and comprehensively
with the excreta of healthy carriers. The two schools of hygienists both confidently claim that their
particular plan of campaign has triumphed.
It is important to note that in the case of both theories there is need for postulating an unknown
causa causans. In Koch's theory this is the something which renders the ordinarily ineffective bacilli
of the healthy carrier effective; in the other theory the unknown cause is that which infects mollusc
or fish in the well, river, or estuary. Again, in the case of both theories the conception that the spread
of the disease is maintained by direct infection from the sick to the healthy is seen to be wholly
inadequate; Koch's followers appeal to the healthy carrier, those who accept the rival theory assume
that the cause of typhoid can develop and multiply outside the human body. There is yet a third
phenomenon which has to be reckoned with by exponents of both theories, viz., the tendency for the
disease to assume epidemic form when circumstances are favourable owing to the existence of unsuitable
methods of excrement disposal, which enable material from typhoid evacuations again to find
its way, it may be after undergoing certain changes, back into the human body, through the mediation
of contaminated water or food stuffs. On Koch's theory it thus becomes necessary to admit at any
rate, a considerable ability on the part of the typhoid bacillus to maintain its existence outside the
human body, and it would seem also necessary to assume that, given "effective" typhoid bacilli, the dose
need only be infinitesimal; on the rival hypothesis a doctrine of multiplication and development of the
causal agency outside the body is appealed to as explaining how it is that, even after the admixture
of enormous quantities of diluting material, the specific poison, say in the oyster or cockle, is still capable
of producing typhoid fever.
There are special difficulties with regard to both theories. Those which arise in the case of
Koch's theory are that the bacillus is very rarely found, where according to the theory, its presence
would naturally be expected, in the shell fish, milk, or suspected water; and on the other hand, it
is especially encountered in unexpected places, bone abscess, gall bladder, healthy carrier, etc., etc.;
moreover, recent research has shown great capacity for undergoing mutation in bacilli of the typhoid
and coli group, a fact which compels some modification of Koch's original views; and most important
of all, the bacillus per se is not, as a rule, effective, its ability to assume pathogenicity from time to time
still remains to be explained. The main difficulty as regards the rival theory was, until recently, proof of
mutation of bacilli resembling the typhoid bacillus, this difficulty at the present moment appears less
formidable than it did a few years ago; the theory, moreover, fits far better than does
Koch's theory the facts as to polluted foreshores and gathering grounds; but two main difficulties
still remain ; there is the question of direct case to case transference, and there is that of the part
played in the transmission of the disease by infected milk, neither of which facts entirely harmonises
with an hypothesis of maturation in the ground, or in the well, or on the foreshore. A question which
presses for settlement, therefore, is as to whether the fresh evacuations of a typhoid patient are potent
for harm—if they are, direct case to case infection may readily occur, and the phenomena of the recorded
milk outbreaks become, perhaps, more easy of explanation. This question is, however, by no means
easy to settle. According to the opinion of fifty years ago, the fresh stools were harmless, some days
in water or earth were needed to develop their potency for mischief ; moreover, Murchison did not
believe in direct case to case infection. The bacteriologists have, of course, changed all that, in accordance
with the theoretical requirements, but it still remains exceedingly difficult to estimate the extent
of risk on the facts. It should be added that there are, in addition to the various problems just referred
to, certain outstanding possibilities which need to be very carefully considered ; for example, the relation
of typhoid fever to those food poisonings of man which are associated with development in the human
body of bacilli allied to typhoid bacilli; and again, the relation of typhoid fever to diseases affecting
the bovine animal and the pig, in which development of certain allied forms of bacilli also occurs.
Observers in various parts of the world have arrived at very diverse conclusions with regard