rally known, that the smoke from the former is immensely
greater than that from the latter, and many old miners date the greater
prevalence of black spit to the introduction of the _linseed_ oil. This
change took place entirely on the score of economy. Any one can conceive
how hurtful to the delicate tissues of the respiratory organs, must be
an atmosphere thickened by such a sooty exhalation.

It is now known, that this disease originates in two principal causes,
viz., _First_, The inhalation of lamp smoke with the carbonic acid
gas[3] generated in the pit, and that expired from the lungs; _Second_,
Carbon, and the carburetted gases which float in the heated air after
the ever-recurring explosions of gunpowder, which the occurrence of trap
dykes renders necessary.

To those acquainted with mining operations, an explanation of the coal
and stone hewing process is unnecessary; but, for the sake of the
uninitiated, I may be allowed to state, in explanation, that, previous
to any coal hewing, it is needful to remove various strata of stone, to
open up road-ways, and break down obstructing dykes, by the aid of
gunpowder. All coal-miners are engaged exclusively with one or other
kind of labour; that is either in removing stone or coal: and the
peculiar disease to which each class is liable, varies considerably,
according to the employment. For instance, the disease is more severe
and more rapid in those who work in the stone, than in those engaged in
what is strictly coal-mining, while, at the same time, both ultimately
perish in consequence of it. The fact of the disease being more acute in
stone-miners, I am disposed to attribute to the carbon and other
products of the combustion of gunpowder, being more irritating and more
destructive to the lungs. A very striking instance of this occurred, a
few years ago, at the colliery of the Messrs Cadell of Tranent. A very
extensive coal level was carried through their coal field, where a great
number of young, vigorous men were employed at stone-mining, or
blasting, as it is called, every one of whom died before reaching the
age of thirty-five years. They used gunpowder in considerable
quantity:--and all expectorated carbon.

It was long a very general belief with medical writers, that the various
forms of discoloration in the pulmonary tissue was induced by some
peculiar change taking place in the economy or function of secretion,
independently of any direct influence from witho