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The same plan that was described above in the case of gaseous disinfectants with regard
to the tubercular sputum, was also followed in the case of the fluid disinfectants, viz., the
materials, wood, linen, paper, cloth, were charged with the sputum, and when dry, exposed to
the disinfectant solution. After the exposure they were well washed in sterile water to remove
the disinfectant, and then the scrapings from the surface of the materials (the dried sputum)
were injected into the subcutaneous tissue of the groin of guinea pigs and the result watched.
We now proceed to describe the results of our experiments, and commence with those
carried out with the gaseous disinfectants, formalin, and sulphurous acid gas.
A. Gaseous Disinfectants.
Series I.—Formalin.
The first experiments were carried out in a room which Dr. Newman had kindly measured
and found to be of cubic capacity of 1344 cubic feet. 30 formalin tablets* were used,
this being in Dr. Newman's opinion, a full allowance for a room this size. The
time allowed was exactly 5 hours. Before lighting the lamp, the window and fireplace were
sealed up with stickfast paper. The lamp was then lit, and the door was sealed up on the outside
with similar stickfast paper. After 5 hours the room was opened, the lamp extinguished,
and the window and door were left partially open all night. The materials exposed to the disinfection
were fetched in the morning and treated in the manner already described.
1.—Bacillus typhosus.
Experiment A.—The materials, wood, paper, linen, cloth were liberally charged with
bouillon emulsion of bacillus typhosus from a 24 hours' old agar culture. The emulsion was
strongly turbid, that is to say, it contained an abundance of the typhoid bacilli. After drying
the materials, they were exposed to formalin, except one sample of paper which was to serve as
control.
After the disinfection (see above), the materials were placed in phenol broth and incubated
at 37° C. After 24 hours the wood, linen, and cloth phenol broths showed much turbidity,
while the paper phenol broth was only faintly turbid, but the control paper showed strong
turbidity. From each phenol broth tube, one phenol agar surface plate was made and incubated
at 37° C. for 24 hours.
The phenol agar plate of wood typhoid showed abundance of colonies which looked, in all
respects, like those of typhoid, the phenol agar plate of cloth typhoid had amongst numerous
colonies some which looked like those of typhoid. The phenol agar plates of linen and paper
typhoid showed no typhoid-like colonies. The phenol agar plate of the control paper broth was
practically a pure culture of typhoid. Sub-cultures were made of the typhoid-like colonies of the
wood and cloth typhoid and they corresponded in every morphological and cultural respect with
those of the true typhoid bacilli. Further, they were tested with blood serum of a guinea
pig immunised by previous injection with typhoid culture and kept in the laboratory for the
general purpose of agglutination (Widal) test. The blood serum was used in the dilution of
1 to 40, i.e., one blood serum to forty emulsion of the microbe to be tested; agglutination of the
bacilli of the emulsion was distinct in 15 minutes, and complete within half an hour.
From this experiment it appears that while the typhoid bacilli on the paper and on the
linen were killed by the formalin vapour, those on wood and cloth had not been disinfected.
The reason for this difference in the two sets is obvious, viz., the bouillon emulsion rich in the
typhoid bacilli readily soaked into the wood and the thick cloth, whereas the thin linen and the
thin paper contained the typhoid bacilli not only in smaller numbers but more exposed. Therefore,
the formalin vapour in this experiment apparently did not reach the bacilli in the depth
of the wood or cloth, while in the thin linen and paper the formalin could more easily and more
readily accomplish the disinfection. Control experiments were made which showed that the typhoid
bacilli are not killed by drying on paper in the air of the laboratory for 24 hours. It must,
however, be at once added that this unfavourable result is not the rule, for we shall presently see
a different result in further experiments. Whether or not the negative result qua disinfection
on wood and cloth in experiment A was due to some fault in the actual experiment, remains
open. As a matter of fact, it was the very first experiment of the whole series.
Experiment B.—In this experiment the emulsion of the typhoid bacilli (agar surface
growth, incubated 24 hours at 37° C.) was made in separated milk, the amount of growth
added to, and shaken up with the milk was considerable, and the emulsion was liberally applied
to the surface of the materials, viz., wood, cloth, linen and paper. The exposure to formalin (5
hours) was carried out in the same place and with exactly the same amounts, and in all respects
in the same way as in experiment A.
The materials next day were placed as in experiment A in phenol broth, which was
then incubated at 37° C. No growth of any kind took place in any of the broth tubes.
Experiment C.—In this experiment the culture of typhoid bacilli was made in gelatine
and incubated for 24 hours at 37° C. After this time the (liquefied) gelatine showed great turbidity,
and in this liquid form was liberally applied to the surface of the materials: wood,
cloth, linen and paper. On cooling, the gelatine set, and in this form was kept a few hours
and then exposed to formalin in exactly the same manner, duration and amount as in experiment
A. Here also the result was complete disinfection of the typhoid bacilli.
The following table I. summarises the above three experiments—
A tablet weighs .034 oz.