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EXPERIMENTS ON DISINFECTION.
Report by Drs. Klein, Houston and Gordon.
In the following pages we beg to report on the experiments which we have carried
out, in conformity with the arranged plan, in order to test various disinfectants, commonly used,
on a variety of microbes, such as would be occurring in practice, and under conditions as nearly
as possible similar to those generally met with.
The disinfectants tested were—(1) carbolic acid, (2) permanganate of soda, (3) bleaching
powder, and (4) corrosive sublimate; these were used in the fluid state as appropriate solutions
to be fully described later. In addition to these, two substances were used in the gaseous state,
viz., (5) formaldehyde, or formalin, and (6) sulphurous acid gas. For the opportunity and
facility of using these two substances we are indebted to Dr. Newman, medical officer of health
of Finsbury, who has been most willing throughout to help us, and who on several
occasions himself superintended the process of disinfection. Dr. Newman has kindly furnished
us with all the details, to be presently mentioned, concerning the amount of the gases used,
cubic space of room, etc. For his help and great interest in the experiments we beg to tender
him our very best thanks.
The microbes that we experimented with were—
(a) Spores of bacillus anthracis, representing one of the most resistant forms of
pathogenic microbes.
(b) The staphylococcus pyogenes aureus, representing one of the most resistant
forms of non-sporing pathogenic microbes.
(c) The bacillus of typhoid fever. Non-sporing forms of pathogenic bacilli.
(d) The bacillus of diphtheria. Non-sporing forms of pathogenic bacilli.
(e) The bacillus pyocyaneus. Non-sporing forms of pathogenic bacilli.
(f) The vibrio of cholera; and
(g) The bacillus of human tuberculosis.
From this list it will be seen that most of the microbes chosen, in the first place include
such as would in common practice be required to be disinfected, and in the second place are
readily identified in the course of the experiment by their colour (staphylococcus aureus, bacillus
pyocyaneus) or by their cultural characters (vibrio choleras, bacillus typhosus, bacillus anthracis)
or by their specific action oil the animal (bacillus anthracis, bacillus diphtheriæ, bacillus tuberculosis).
These are advantages which are not to be under-rated, considering that the materials
subjected to disinfection are not themselves sterile, and are for hours exposed to mixture with
saprophytic bacteria, conditions which naturally increase the difficulties of subsequent identification
of the particular microbes subjected to disinfection.
The microbes enumerated above were in all instances (except the spores of bacillus
anthracis and the bacillus tuberculosis) 'taken from a recent actively-growing culture (agar
culture grown for 24 to 48 hours at 37° C.) so as to ensure the active and vigorous state
of the microbe to be disinfected. This is a point to be borne in mind, being of importance in
all disinfection experiments. It must be obvious that in all cultures of non-sporing microbes,
many of the individual microbes become less vigorous, and others even die off with the age of the
culture; thus, for example, in the case of bacillus diphtheriæ, the virulence of the microbe
becomes, in agar culture grown at 37° C., rapidly attenuated after the first two or three days;
bacillus typhosus taken from a 24 to 48 hours' agar culture shows all bacilli actively motile;
later, the number of such acting motile forms rapidly diminishes, indicating that the bacilli with
age of the culture undergo distinct changes, whereby some of their important characters are for
the time lost. As regards the spores of anthrax, these, as is known, are formed in the course
of several days to a few weeks on the surface of the agar growth. The spores used in our
experiments were ascertained to be fully virulent on the animal. The bacillus tuberculosis was
used as it occurs in human pulmonary sputum, this being not only the form in which this
microbe would be dealt with in actual practice, but also the form known to be virulent, and
therefore suitable to be subjected to disinfection.
The experiments having been undertaken to ascertain which of the substances commonly
in use are best for the object of disinfection under conditions such as exist in actual practice,
it was of course necessary so to arrange our experiments that they would, as far as possible,
imitate the conditions commonly obtaining. For this purpose we distributed the microbes on
various materials, such as wall-paper, linen, cloth and wood, these being the chief materials
which in ordinary practice are subjected to the process of disinfection in rooms, tenements and
inhabited spaces.
The modus procedendi was this—
(a) Virulent spores of anthrax taken from the surface of agar cultures were
distributed in separated milk, or in melted gelatine, so as to form a turbid emulsion.
This emulsion was applied liberally on the above materials and allowed to dry in the
air of the laboratory.