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35
Dr. Betty Hobbs later reported as follows:—
"A summary of our findings up to date is given below:—
"The effect of different temperatures of storage on germination
of the spores and the multiplication of the bacillary forms of CI.
welchii inoculated onto slices of freshly boiled lamb and into gravy
was investigated in the School Kitchen.
"Legs of lamb boiled on the morning of the experiment were
sliced automatically at about 10.30 a.m. Three slices were placed
into each of four tins and each slice was inoculated with approximately
10,000—16,000 viable spores (two experiments), or
approximately 260,000 viable organisms including bacilli and spores
(one experiment).
"The tins were left in the hot-plate, on top of the hot-plate
with and without gravy and at room temperatures. The three
slices were removed at hourly intervals and stored in the cold
pending examination, temperatures were recorded at the same time ;
control slices of inoculated and uninoculated meat were also
examined. Gravy was inoculated immediately after preparation
and allowed to stand on the hot-plate for three hours. Portions
were removed each hour. Ultimately the gravy was incubated
overnight and examined the following day. The temperatures varied
from 39°—49°C. on top of the hot-plate, from 62°—94°C. inside
the hot-plate and from 18°—26°C. in the kitchen.
"The results were most striking from the meat slices inoculated
with mixed bacilli and spores. The count of C1. welchii for those
standing on top of the hot-plate without gravy increased to 19.5
million in three hours, the count for those on the hot-plate with
gravy increased to 2.5 million in two hours and 46 million in three
hours ; there was no corresponding rise in aerobic organisms.
"Inside the hot-plate conditions were evidently lethal, because
no count was obtained from these slices.
"At room temperature the counts remained the same throughout,
there was neither rise nor fall.
"In the experiments where spores only were used the inoculum
was too low and although the trend was the same, that is, germination
of the spores and multiplication of the resultant bacilli on the
slices kept in gravy on top of the hot-plate, the results were not so
striking. Increase in the count of CI. welchii in the gravy was
shown only when the inoculum was a mixture of bacilli and spores
when the count increased from 500 per ml. to 100,000 per ml. in
three hours. After overnight incubation at 37°C., however, the
gravy counts in two experiments were 105 and 250 million per ml.
of gravy.