June 14, 1918.

THE COLLIERY GUARDIAN.

1207

THE EFFECTS OF DUST INHALATION.*

By J. Scott Haldane, M.D., F.R.S.

Th© disastrous effects produced by inhaling certain
kinds of dust are now only too well known in mining
communities. It is equally well known that no evident
ill effects result from inhaling certain other kinds.
Thus coal-mining in Great Britain is on the whole a
very dusty occupation; but there is no evidence in the
mortality returns for either young or old colliers that
dust-inhalation has hitherto caused appreciable danger
to life in British coal-mining. The wide-spread intro-
duction of stone-dusting for preventing coal-dust explo-
sions has, however, directed new attention to the
possibility of injurious effects of dust-inhalation in
coal mines.

The ill effects from dust-inhalation in mining have
only been observed where hard rock is mined, and
practically speaking only where the rock is quartz, or
stone, such as granite, containing quartz. Observa-
tions not merely on miners, but also on other persons
not exposed to dust from various forms of quartz or
crystalline silica all tell the same story of dangerous
injury to the lungs, and death from phthisis after pro-
longed inhalation of quartz-dust. The natural infer-
ence from these observations would seem to be that
dust-inhalation is dangerous in proportion to the
amount of quartz or silica inhaled, but the author has
met with many instances where men were consider-
ably exposed to siliceous dust, without injury.

When stone-dusting with shale-dust was first intro-
duced by Sir William Garforth, it was generally
believed that the shale contains practically no crystal-
line silica, but only silicates, but Dr. Mellor found 35
per cent, of quartz in the Altofts shale, and investi-
gations by Prof. Sollas, F.R.S., gave just about the
same quantitative result. It may therefore be
accepted as a fact that even the softest shale contains
about a third of its weight of crystalline silica in fine
particles. Nevertheless, the statistical evidence shows
that inhalation of shale-dust is harmless in practice.
A few years ago it was tacitly assumed that the black
dust lying along the roads and working-faces of coal-
mines is, practically speaking, pure coal-dust; but, as
a matter of fact, the black dust actually present on
the roads and at the face is hardly ever pure coal-dust,
being usually a mixture containing a high percentage
of stone-dust—often sufficient to make dust explosions
impossible.

Natural Stone Dust in Coal Mines.

Investigations made on the establishment of the
Doncaster Coal Owners’ Laboratory showed that along
the roads and faces of their pits the black dust con-
tained a high percentage of stone-dust. At Bentley
Colliery, for instance, there was about 50 per cent, of
stone-dust in the small quantity of fine dust along the
faces; and except near the pit-bottom the percentage
along the roads was about as high, or higher. The
late Mr. J. W. Fryar then arranged for the
systematic collection of samples from a number of pits
in the Nottingham district, and the analyses at the
laboratory of 170 samples from eight different seams
gave the following average results for the dust passing
a 90-mesh sieve:

Places at which samples were taken.	Roof.	Sides. Floor.	
200 yds. inbye of pit-bottom ...		 41*2	... 36*1 ...	33'6
Half-way to face			 38’1	... 42 T ...	37'7
200 yds. from face 			 50’7	... 56’2 ...	51.0
The Nottingham district	has been	practically	free

from dust explosions, so it must not be assumed that
so much stone-dust would be present in other mines.
The percentage is certainly often a good deal lower.
But it is at least evident that for many generations
all coal miners must have inhaled a great deal of stone-
dust, and therefore a great deal of crystalline silica.
The stone adjacent to the Nottingham coal-seams is
often full of crystalline silica, and almost more a
sandstone than a shale. A sample examined by Mr.
J. Ivon Graham at the Doncaster Laboratory showed
over 70 per cent, of silica. Now in the Nottingham
and Derby district the death-rate among miners from
lung diseases is, at all ages up to 55, not only, as
with all coal miners in England, far below the average
for other employments, but even slightly lower than
for farm labourers. The death-rate for phthisis alone
is also slightly lower than for farm labourers. Among
metalliferous miners living in Cornwall, many of whom
had worked in the Transvaal, the corresponding death-
rate . from lung disease was, at middle age, about
fifteen times as great as among the Nottingham
miners, and more than thirty times as great as’ their
accident death-rate. It seems to the author probable
that the Nottingham coal miners inhale about as much
crystalline silica as metalliferous miners; but there
are no ill effects at all.

In gold-mining in quartz reefs there seem also to
be striking differences at different places as regards
the danger of the work. At the Mysore mines, for
instance, where the gold is in quartz, there is but
little trouble from lung affections attributable to dust;
and in Western Australia there appears also to be only
a moderate amount of trouble. In the Transvaal, on
the other hand, the trouble has been of a most for-
midable kind, necessitating extremely drastic preven-
tive measures.

The ill effects of quartz-dust have been attributed to
the sharpness of the particles, and their consequent
irritant action on the lungs. But if so, one would
expect the quartz-dust to prove irritant in propor-
tion to the amount inhaled. One would also expect
to find sharp spicules in the lungs, whereas what is
actually found consists of extremely fine particles,
which do not look specially sharp or different in
appearance from other very fine particles.

Experiments on Animals.

The whole matter was so mysterious that it seemed
very desirable to try to clear it up by experiments
on animals, and the Medical Research Committee
under the National Insurance Act asked the writer

* From a paper presented to the Institution of Mining
Engineers.

to arrange for the investigation, and provided the
necessary funds. The work was carried on in the
writer’s laboratory at Oxford by Mr. A. Mavrogor-
dato, and short references to results reached up to
date were made in the report presented to the Explo-
sions in Mines Committee in 1915.* Unfortunately,
the war has put an end to the work for the present.
Before leaving it in order to take up other medical
work connected with the war, Mr. Mavrogordato had,
however, so far completed essential parts of the inves-
tigation that he was able to prepare a report to the
Medical Research Committee, and this report is in
process of publication in the Journal of Hygiene.

The experiments were, like those reported by Prof.
Beattie to the Explosions on Mines Committeef made
on guinea-pigs; and they confirmed in all respects
Prof. Beattie’s conclusion that the inhalation of shale-
dust in amounts such as a miner would probably be
exposed to is practically harmless.

Effect of Dust Particles on Lungs.

It appears that any kind of dust-particles (except,
perhaps, when they are soluble and chemically harm-
less) will cause inflammatory changes in the lungs if
enough of the particles are inhaled. The nose and
air-passages are, of course, a great defence against
dust, and in some animals the convoluted surfaces
inside the hose constitute a particularly efficient
defence. The particles which fall against the sur-
faces of the nose and air-passages are swept out by
the action of the cilia -lining these passages, or by
coughing, etc. Nevertheless, a considerable portion
of the very finest dust reaches the lungs, and will
cause harm if it is in sufficient amount. This harm,
if caused immediately, seems to be much about the
same with all sorts of dust. But if the harm is not
caused immediately, there is a great difference in the
effects. Certain dusts, and notably any unmixed form
of crystalline silica, cause lasting and cumulative
injury; whereas others, and notably coal-dust or shale-
dust, cause no cumulative injury, and no injury at all
unless they are present in enormous amounts.

Now, what happens to the dust within the lungs in
these two cases? On this point the experiments gave
a perfectly clear answer. When the animals were
exposed to as nearly as possible equal quantities of the
fine dusts, and for equal times, the dusts were, at the
end of the period of exposure, found to be abundantly
present in the lungs. With coal-dust there was special
abundance, which is what would be expected,^ con-
sidering its lightness and fineness. The lungs became
quite black. But if the examination was made some
weeks later, it was found that the coal-dust and shale-
dust lungs were clearing up, whereas there was no
evident diminution in the dust in the lungs of animals
which had been exposed to powdered, flint or quartzite
dust from a Transvaal gold mine. After several
months the coal-dust and shale-dust had entirely dis-
appeared from the lungs, whereas the flint and
quartzite were nearly as abundant as immediately
after the exposure to the dust.

The examination showed that all . the dust particles
are taken up into the protoplasm of certain of the
epithelial cells lining the air cavities of the lungs. In
the case of the coal-dust or shale-dust these cells
detach themselves and wander away with their load
of dust particles. Some pass directly into the ends
of the bronchial tubes, and are thence swept upwards
by the cilia and swallowed. They thus pass out of
the body by the alimentary canal. Other dust-laden
cells wander into the lymphatic vessels, and are car-
ried to the lymphatic glandular tissue surrounding
bronchi. From this position they wander right
through the walls of the bronchi, and are then swept
out like the cells already referred to. Still other
dust-laden cells are carried into the lymphatic glands
at the roots of the lungs, and where they wander after-
wards is still uncertain.

In the case of the flint or quartzite dust nearly all
the dust remains in situ. It is only to a comparatively
small extent that the cells wander out with it, although
some wandering does occur, and some of the dust
gradually reaches the lymphatic glands, where it can
readily be recognised, as it becomes coated with a
dark pigment.

It can now be realised readily what is happening
in the lungs of a coal miner breathing large quantities
of coal and shale-dust, as compared with what is hap-
pening in the lungs of a gold miner breathing quart-
zite dust. As fast as the dust goes in day by day to
the coal miner’s lungs, it is carried out again by the
dust cells. His lungs, it is true, are probably always
more or less black; but, on the other hand, what he
coughs up is black and full of the dust on its way out
again. His black spit is in truth his salvation. On
exposing the animals to relatively small daily doses
of coal or shale-dust, and continuing this over a long
period, it was found that after a few days the dust
in the lungs ceased to increase. The intake of dust
was thus balanced by the output. From all that is
known about similar physiological processes, one may
be fairly sure that the capacity for eliminating dust
particles grows with use. If this is so, the practice
of constantly getting rid of coal and shale-dust may
help the lungs in eliminating other kinds of harmful
particles, such as tubercle bacilli, and may thus
account for the remarkable fact that coal miners are,
and always have been since statistics were first avail-
able sixty years ago, extremely free from phthisis.

Quartzite Dust.

In the case of the miner breathing quartzite dust,
the dust remains for the most part in situ in the lungs,
and there tends to accumulate from month to month
and year to year. Some of it is certainly got rid of;
but in order to reach a balance between intake and
output, without there being a dangerous permanent
loading of the lungs with dust, the amount of dust
inhaled must be reduced to a minimum. The fate of

* Seventh Report of the Explosions in Mines Commit-
tee, Parliamentary Paper [Cd.S. 122], 1915.

+ First Report of the Explosions in Mines Committee,
Parliamentary Paper [Cd.6,307], 1912.

men who have constantly, and often against constant
warning and against the law, exposed themselves to
heavy concentrations of quartzite or granite dust in
working rock-drills and in blasting is tragic. The
information obtained by local registrars in Cornwall
as to the mining history of miners who have died there
shows that, previous to the war, the average duration
of employment on machine-drills of the men who died
in the Redruth area, and had worked machine-drills
in the Transvaal only was 4-7 years, and for those
who had worked machine-drills in Cornwall only was
7-8 years. Practically every one of these men died of
phthisis, and usually at an age below 40.

With regard to the ultimate effects of chronic over-
loading of the lungs with dust, it may suffice to men-
tion that an over-development of connective tissue
gradually occurs, constituting the condition of
“ fibroris,” and that at the same time the lungs become
extremely susceptible to attacks by the tubercle
baccillus, so that death from phthisis is the usual
result.

Process of Elimination.

Why is coal or shale, dust easily removed from the
lungs, but not siliceous dust? And why, above all, is
pure quartz so difficult to remove, while the large
proportion of quartz in shale-dust is removed quite
easily? As regards the first question, the evidence
points to the fact that not only is quartz dangerous,
but also other kinds of very insoluble crystalline dust.
Thus Prof. Beattie found that emery (a crystalline
alumina) and carborundum (a carbon silicide) are
very dangerous. Now, if it were the case that the
danger is due to mere hardness or sharpness, we should
expect to find that crystalline dust, even when mixed
with other dust, is dangerous. But the quartz in
shale and other hard stone is actually harmless in
practice. The mere chemical composition of the stone
does not seem to matter. There is, however, a quality
in the dust that does seem as if it mattered, and this
is its power of adsorbing other substances.

Adsorption or solid solution is a process distinct from
chemical combination and similar to solution in a
liquid. It depends upon attraction between the mole-
cules of the adsorbed substance and those of any free
surface on or in the adsorbing solid, just as solution
depends on attraction between the molecules of the
solvent and of the dissolved substance. Particles of
coal-dust and other insoluble carbonaceous matter
possess in a high degree the property of adsorbing
other substances. The same property is possessed in
a less degree by such substances as shale; while crystal-
line substances, such as quartz, seem to have very
little adsorptive power.

Now, it can well be imagined that insoluble dust
particles are attractive and stimulating to dust-col-
lecting cells in proportion to the soluble substances
adsorbed in the dust particles, and that the particles
containing little of these substances will be correspond-
ingly unstimulating. This, at least, seems the most
probable explanation of why some kinds of insoluble
dust stimulate the cells and others do not; and the
facts so far known seem to be consonant with this
explanation, although far more work on the whole
subject is required.

To the second of the two questions the answer seems
simpler. The particles of quartz are taken up by
dust-collecting cells, as already mentioned, although
the cells do not readily wander out with them. But
if enough of the juicy adsorbent particles are also
present, they will stimulate the cells sufficiently, and
consequently the whole of the dust, including the
quartz, will be removed. In this way it can be seen
how a mixture of quartz with silicates, as in shale-
dust and the dust from many hard stones, causes no
harm. It can also been seen why the dust in the
Transvaal gold mines is so much more harmful than
in some other districts where the metal mined is also
in quartz. In the Transvaal both the gold-bearing
reef and the surrounding country rock is quartzite.
The quartz-dust is thus very pure. At Mysore, on
the contrary, the country rock is not quartzite; and
the dust is therefore a mixture containing, probably,
enough of the stimulating variety of dust to stir the
dust-collecting cells to activity.

On the subject of the Mysore mines and the country
rock of the Transvaal mines, Dr. W. F. Smeeth, of
the Mysore Government Mines Department, has
written the following as regards the Mysore mines:

The auriferous veins are composed of practically pure
quartz; but the rock or “country” in which the veins
lie is composed of basic lava flows having about the
following composition : SiO2 = 49 per cent. ; A12O3 = 14
per cent. ; Fe2O3 and FeO = 14 per cent. ; MgO = 6 per
cent.; CaQ = 11 per cent.; Na20 and K20 =3 per
cent. ; etc. Owing to the small size of the veins a good
deal of the “ country ” is broken along with the quartz—
perhaps 30 to 50 per cent, of the former; and the dust
is likely to consist of not much more than 50 per cent, of
quartz, with nearly 50 per cent, of silicates.

Effect of Mixed Dusts.

If the presence of another dust can prevent the ill
effects of quartz or other dangerous varieties of dust,
then one should expect to be able to verify this by
experiment; and Mr. Mavrogordato was able to carry
out experiments where coal-dust was added to the
flint-dust breathed by the animals. The results
indicated that practically the whole of the flint-dust
was got rid of within a moderate time.

Unfortunately, these very important experiments
have had to be postponed. It is evident, however, that
the facts ascertained point to the possibility of attack-
ing the problem of dangerous stone-dust in ^lines and
elsewhere from a new side, and in a manner strangely
similar to that in which Sir William Garforth attacked
the coal-dust problem. If the inhalation of dangerous
stone-dust cannot altogether be prevented, its effects
can apparently be neutralised by causing another kind
of dust to be inhaled along with it. Dust from pul-
verised clay or shale, or a mixture of coal-dust with
shale-dust, would seem to be suitable. A black mix-
ture of, say, 60 per cent, of shale with coal-dust might
be specially suitable, as it would be easily visible, and
could not explode. The most suitable method of