Scientific Memoirs by
factive processes are initiated under anaërobic conditions, should, find the condi
-tions more propitious. But B. coli is a sanitary bugbear in virtue of its associa
-tions and it has yet* to be proved that it can per se produce enteric fever, by a
progressive property of infectiveness; at any rate it is abundantly present as a
normal guest in every human intestine. What we can say amounts to this,
that the sojourn of fastidious parasites in an anaërobic tank exposes them to
such unfavourable conditions, mechanical, (from sedimentation and a course of
upward and downward filtration), chemical and biological, that the chances of
ultimate survival in the final effluent are exceedingly poor and doubtful. The
fate of pathogenic organisms in the dead animal body under anaërobic conditions
affords striking testimony in favour of this view.†
Cartwright Wood and Sims Woodhead found in certain experiments, that crude
sewage containing 500,000 organisms per c.c., when inoculated into the filtered effluent of a
septic tank, developed more than 1,000 millions per c.c., in a few days—saprophytes
which would be very injurious to any parasite. Sims Woodhead concludes "that
none of the organisms contained in the effluent are themselves capable, in the quantities
present or to which they can grow even in broth, of setting up any morbid changes."
In the same Local Government Board enquiry, Pickard investigated B. typhi, with
reference to the action upon it of crude sewage, and to the effect of fitration on the few
germs (B. typhi), that had survived a short exposure to sewage. He concluded "that sew
- a g e e v e n w h e n s t e r i l i z e d w a s n o t o n l y a b a d f o o d , b u t a n a c t u a l p o i s o n " t o B . t y p h i ;
that in the septic tank they suffred rapid extermination, and that filter beds act as a
further safeguard, "so that there is no chance whatever of a filtered effluent causing
enteric fever if passed into a river."
Lawes and Andrewes had previously shown that certain liquefying organisms
(of which there are an untold number in a septic tank or bed) have a germicidal
effect on B. typhi, so that their survival through the anaërobic process of
putrefaction is almost certainly precluded. In a recent report made to the L. C. C.,
October 1899, Dr. Houston thus summarises his opinion on this question:
"it is to be noted that the biological treatment of sewage is conducted under control; second
- l y , t h a t t h e p r o c e s s a l w a y s g r a d u a l l y s e c u r e s t h e d e s t r u c t i o n o f t h e p a b u l u m o n w h i c h t h e
bacteria feed, and hence leads to their death; thirdly, that the balance of evidence points
to the probability that some of the pathogenic organisms are crowded out in the struggle
for existence in a nutritive medium containing a mixed bacterial flora, their vitality being
weakened or destroyed by the enzymes of the saprophytic species; fourthly, that the che
- m i c a l p o i s o n s p r o d u c e d b y b a c t e r i a a r e h i g h l y u n s t a b l e a n d r a p i d l y b r e a k d o w n i n t o t h e i r
innocuous constituents; and, lastly, that in some cases it may not be necessary to attempt
the complete purification of the sewage, the solution of the suspended matters and
partial destruction of putrescible matter in solution being all that is urgently called for,
as for example where the effluent is of relatively small bulk and is turned into a stream,
the water of which is not used for domestic purposes, or else, where the effluent is to be
subsequently treated by land irrigation. "
* Horton-Smith, 1st Goulstonian Lecture; "Lancet," March 24, 1900, page 821.
† See Klein, Appendix B, No. 2, Report of Medical Officer to L. G. B., 1898-99.
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