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52
man by slightly tapping the tin with the hand. It gives a note different from
that given when a sound tin is struck. The note is more resonant, and,
speaking musically, it is half a tone to a tone higher in the scale than that of
a sound tin. A similar effect is produced when the human chest is percussed,
Only conversely. That is, the Physician diagnoses a consolidation of the lung,
when a duller sound is produced on percussing the chest with the fingers, than
is given when the person examined is healthy. The sound given by striking
the blown tin is more resonant, because it contains gas, and that of the chest
is less resonant because there is less air present than in the healthy Lung.
There is another factor that causes the tinned food to be dangerous,
although the food itself appears perfectly wholesome, and there is no sign of
decomposition. This occurs when the canning is old, and some of the tin or
lead, which is used to solder the lid, has been dissolved.
During the last few years I have frequently analysed the contents of old
tins which were found to contain such large quantities of tin, together with
occasionally small quantities of lead, as to be positively dangerous. The tins
show no sign of bulging, and when they are opened the contents appear
wholesome and taste as well as any fresh cooked meat. It is sometimes very
difficult to persuade the owners to surrender such goods, and it is only when I
absolutely refuse to allow them to be removed, and I threaten to have them
taken to the Police Court to be condemned by the Magistrate, that the owners
consent to submit them to their own analyst for examination, and ultimately
surrender them.

The presence of a trace of lead was detected in the tinned Salmon only.
No trace of it could be discovered in the others.