The influence of dust inhalation upon the incidence of phthisis

PUBLIC

!92I.

THE INFLUENCE OF DUST INHALATION ~3PON THE INCIDENCE OF PHTHISIS.* BY

EDGAR L . COLLIS, M.A., M.D., M . R . C . P . , Mansel T a l b o t Professor of P r e v e n t i v e Medicine, W e l s h N a t i o n a l School of Medicine. Predisposition is t o - d a y the key note to the tuberculosis problem. E r a d i c a t i o n of the infecting agent, the tubercle bacillus, is not a practical proposition in the same way that the infective agent of yellow fever or of m a l a r i a m a y be eradicated by destruction of mosquitoes, that of typhus by war upon the body louse, or t h a t of enteric fever by ensuring a pure w a t e r supply. F u r t h e r , even if eradication could be ensured, the question would arise as to how great the final benefit to the comm u n i t y would be, since tuberculosis is for the most part an index disease, that is it is closely correlated with the d e a t h - r a t e from all other causes, and its prevalence is a direct indication of the prevalence of sub-normal health in the community. G r e a t e r benefit must follow from increasing the resisting power of the nation, so that not only tuberculosis bht other forms of disease as well, are held at a r m ' s length. T h e r e is definite evidence that just as typhus has gone from this country and typhoid is rapidly disappearing, so, although we are uncertain as to the reason, phthisis also is diminishing, while simultaneously the general d e a t h - r a t e has been falling. TABLE I.

COMPARATIVE MORTALITY OF ENGLAND AND WALES SINCE 1851. MALES.

Period. 1851-60 I861-70 1871-80 1881-90 1891-1900 1901-10

~EMALES.

Phthisis. All Causes. .. .. .. .. .. ..

Fall in 50 years

100 97 88 73 61 50

.. .. .. .. .. .,

50% ..

t00 102 99 90 88 75

Phthisis. Alt Causes. .. ., ., .. .. ..

25% ..

106 96 79 62 46 35

.. .. .. .. .. ..

67% ..

91 91 85 78 75 62

32%

NB.--The death rates are expressed as percentages of the male rate for 1851--60 which was for All Causes 22-1 per 1,000, and for Phthisis 2"6 per 1,000.

T h e figures given in the table show how phthisis continues to be a pointer to influences which lower resistance to disease. A m o n g these influences the condition of the a t m o s p h e r e stands p r o b a b l y first. T h a t it does influence general health is indicated by analysis of m o r t a l i t y d a t a , A paper read before the Tuberculosis Group of the Society of Medical Ofticets of Heaith, on January I4th, I92t.

HEALTH.

97

such as that m a d e by B r e n d (1), w h o concluded that excess of infantile m o r t a l i t y is due to some factor or factors in industrial towns, the centres of large cities, and m i n i n g areas, of which possibly the most important is the polluted state of the atmosphere. S i m i l a r conclusions as to the influence of a t m o s p h e r i c conditions follow from analysis of adult m o r t a l i t y data. B u t the influence of the a t m o s p h e r e on general health, and particularly on the incidence of tuberculosis, is a large subject upon which I am not e m b a r k i n g . My intention is only to refer to the influence of dust particles which m a y be inhaled. Some apology might be needed from me in yenturing to deal again with this a s p e c t of tuberculosis. B u t there seems to be still some lack of a p p r e c i a t i o n as to w h e r e we stand to-day in relation to the matter, and also there is some new evidence to report. H e n c e I venture to return again to the subject. P a r t i c u l a t e m a t t e r which m a y be inhaled is as various in its composition as that of m a t t e r in general. I t m a y be composed of (a) viable cells, i.e., micro-organisms ; (b) dead animal or vegetable substances, or (c) inorganic material. E a c h group, from the point of view of inhalation, is important.

Viable Particles.--The only m e m b e r of this g r o u p i s the tubercle bacillus itself. S o m e authorities, I a m aware, favour the intestinal tract as the main portal of entry, and hold that p u h n o a a r y tuberculosis results from a l i m e n t a r y infection which m a y have taken place y e a r s before, I may Personally be p r e j u d i c e d against this view since I recall (1) how industrial lead poisoning used to be ascribed in the main to m a t e r i a l which was swallowed, until G o a d b y showed t h a t poisoning followed upon inhalation of one hundredth p a r t of the dose necessary if a d m i n i s t e r e d by mouth ; and (2) how C a l m e t t e at one time claimed that dust found in the lungs d~d not get there through direct inhalation, but only via the digestive tract. Certainly there stands the undoubted fact that animals can be infected aerially. U n t i l proof to the c o n t r a r y is forthcoming t incline to the view that adult phthisis as seen in industries is a new infection, probably air borne. F o r the m o m e n t i a m content to lay stress on the fact that, other things being equal, phthisis a m o n g adults is more p r e v a l e n t in crowded communities, where e x p o s u r e to direct infection is m o r e possible. T h e t h e o r y of adult infection m a y be held to receive s u p p o r t

PUBLIC H E A L T H .

98

from the unusual mortality from phthisis experienced in sedentary or semi-sedentary occupations, such at shoe-making, printing, and tailoring, wherein aggregation of individuals seems to be one factor distinguishing the conditions from those of other occupations. A number of other possible factors have been considered (2) :--fatigue, hereditary predisposition, poverty and consequent malnutrition, alcoholism, housing, infection from materials used, legal overcrowding, cramped position at work, and sedentary character of work ; only to be rejected when these industries are compared with other occupations with lower mortality from phthisis. Thus to take two only :--the claim that phthisis is here a pestis pauperum fails, for the shoemaker certainly receives no less a wage that operatives employed in the manufacture of hosiery. While the physical attributes of the atmosphere are not more unfavourable than in textile industries where the incidence of phthisis is not abnormal, but where individuals are fnrther separated, h4 the three industries named in the preceeding paragraph phthisis is the only great cause of death markedly in excess, so that difficulty arises in accepting the view that the excess is due to general lowering of resistance to disease. When general resistance is lowered, as by alcohol, every cause of death should, on theory, be found in excess, and indeed this is found to occur among innkeepers and publicans. (See Table 2). When general resistance is increased as by outdoor life, every cause of death should be found diminished, and this is found to occur among agricultural labourers. T A B L E ' 1 I. MORTALITY

COMPARATIVE

IN

CERTA1N

OCCUPATIONS, 1900-02.* Class ALLMALV:S

..

186

Labourer' h~ Agricultural Districts .. 75 Coal Miner (Lancashire) 98 Wool,'vVorsted operative., 161 Hosiery operative . . 9.00 Cotton operative .. 214 Innkeeper, Publican .. Tailor . . . . Shoemaker .. Potter .. Printer .. Cutler .,

Tin Miner * Figures

D i s e a n e s of t h e Nervous Circulatory Respiratory Systems."

Phflfisis

232 2~a 2~7 291 323 506

. . 851

All Causes.

..

105

..

144

..

174

..

1,000

..

52

..

102

..

80

..

567

..

77

..

1'2t

,.

26t

..

939

..

92

.,

150

..

155

..

917

..

93

..

129

.,

142

.°

862

..

100

..

140

..

t99

..

t,010

.. .. .. ... .. .. ..

tlI~ 89 83 98 71 105 77

.. .. .. .. .. ,. ..

209 123 136 199 107 20tt 161

.. .. .. .. .. ,. ..

260 145 140 125 1t0 300 735

.. .. .. .. .. .. ..

t,709 950 916 t~372 903 t,468

above the standard set by All Males are printed in h e a v y t y p e .

2,160

MARCH,

When local resistance is lowered as in the case of the cotton operative by cotton dust, of the cutler, potter and tin miner by silica dust, and of the coal miner by rock dust, the effect is to increase tile incidence of diseases which attack the locality concerned, in this case the respiratory organs. (3) But if we postulate merely increased exposure to a definite infection, tile only result to be anticipated is increase of the disease caused by the infecting organism; and the mortality data of shoemakers, printers and tailors appear to present instances where this exposure to an undue amount of infection with tubercle bacilli exists. I have previously referred (4) and shall refer a~ain later to this method of statistical differential diagnosis ; for the moment I ask for consideration of ttle evidence it appears to give in support of direct personal infection with tubercle bacilli, probably air borne.

Dead Animal and Vegetable Substances.--This group is promising to be one of great interest. Evidence is gradually accumulating to show that so far as phthisis is concerned, dusts belonging to this group fatt into two classes, one including dusts which are innocuous, and the other incIuding dusts which may be positively beneficial. As long ago as 1913 when dealing (5) with the effect of dusts in producing diseases of the lungs, I suggested that dusts appear to be more injurious as their chemical composition differs from that of the human body, or from the elements of which the body is composed. The chemical composition of this group of dusts is closely allied to that of the body. And the evidence before us is that no class of persons exposed to the inhalation of this group of dusts is known which experiences a high incidence of phthisis, unless that incidence can reasonably be ascribed to other influences. The possibility of dusts belonging to this group acting as carriers of tubercle bacilli cannot be neglected when considering either this group or indeed any other group of dusts. Theoretically any form of dust may thus assist in the dissemination of tubercle; but I know of no definite evidence bearing on the question. Consideration of this carrier possibility belongs rather to the question as to whether pulmonary tuberculosis arises from aerial infection. If we accept this possibility then we may reasonably accept that infected dust particles, as well as isolated bacilli, may give rise to infection.

PUBLIC

I92I,

The

evidence

that

some

organic

beneficial rests on the prevalence

dusts

may

be

phthisis experienced

low

death

( s e e Table 3), n o t

also

abroad,

compel

definite

us

to a d m i t

inhibitory

the

shall

proposal

has

gold-mines

with

fever

made coal

upon

FROM

the

to

galleries

of

prevent

miner's

AMONG

COAL

Comparative mortality figure,

MORTALITY

.. ..

34 35

450 255

.. ..

84 88

.. .•

31 to 32 37 to 38

434 269

.. ..

93 96

.. ..

34 to 35 38

Occupied a n d Retired Males . . . . . . 64,097

..

187

..

38 to 39

79 144

.. ..

53 70

.. ..

29 to 30 34

541

..

70

..

31 t o 3 2

..

46 to 47

.. .. ..

54 71 71

.. .. ..

49 to,g0 44 t o 4 5 51

.. ..

108 149

.. ..

42 to 48 43 to 44

.•

92

..

49 to 50

77 67

.. ..

34 40

.. ..

49 to 50 47 to 48

379 317

.. ..

g4 69

., .,

51 48to49

457 137 366

.. .. ..

69 70 100

•. .. ..

45to46 48 to 49 48

Occupied a n d "Retired Males . . . . . . 32,628

..

67

..

51 to 52

Derbyshire .... Nottinghamshire .. Durham and Northumberland . . . . . . Yorkshire.. M o n m o u t h s h i r e ' " a n'~i South Wales .... Staffordshire .... Lancashire .: ..

inhale

ganister

mortality

.. .. .. ..

70 74 81 107

.. .. .. ..

37 34 to35 36 to137 40

..

142

•.

38 to 39

from

coal dust

exerting

a

dust

tubercular

is m i x e d w i t h

second

grade

suffer

influence

are

.grouped

referred to again later.

underground

far apart;

and

there

on

is b u t

the little

Two other

little is known dusts

influence.

The

infection.

Ten

ago all forms

Recent

investigation

industry

(6) h a s

phthisis

mortality

brought among

in

the

iron

and

steel

as dangerous.

subject Then

this

do

on

not

have

pottery

clay

because their

This

their

containing

matter will be

to-day of the possibility of

in this group,

personal contact, but little possibility of passing on

years

if

making

to p o t t e r s .

here

depends

certain organic constituents.

Both

but

is in

fireclays ; certainly

probably

excessive

loses its perniciou~

does not render flint dust harmless

i n f l u e n c e r e q u i r e s to b e c a r e f u l l y l o o k e d in w h i c h

it

All clays

must

not be lost of the way

as

bricks, the dust

effect, only

an

sillicosis;

(See Table 6).

character

from

fireclay

into, sight

work

Median a g e at de~,th.

g2

favourable

they

COAL

..

Fireclays of

scarlet

AMONG

Comparative mortality figure,

Nottinghamshire a n d Derbyshire .... 114 Durham and Northumberland . . . . . . 228 Yorkshire .... t95 Staffordshire 117 M o a m o u t h s h i r e ' " a n'~i South Wales . . . . 456 Lancashire .... 870

stone

possibility

and

communicable

PNEUMONIA MINERS.

Coal field.

this

work.

also

Ganister B r i c k s . - - G a n i s t e r is a q u a r t z i t e r o c k , i.e., it i s a f o r m o f p u r e s i l i c a , a n d t h o s e w h o

1910-12.

surface

men

1910-12.

64 66

Occupied a n d R e t i r e d Males . . . . . . 58,492

FROM

Occupied and R e t i r e d Males . . . . . . 35,5t7

Median a g e at death.

.. ..

476 155 404 36g

directly

1901-02.

that the

t60 119

Nottinghamshire .. Derbyshire .... Durham and Northumberland . . . . Monmouthshire'" a n d S o u t h W'ales . . . . Staffordshire .... Yorkshire . . . . . . Lancashire ....

the diseases

later

1II.

Total No. of deaths,

Nottinghamshire a n d Derbyshire .... Staffordshire .._. D u r h a m and N o r t h u m berland . . . . . . Yorkshire.. Monmouthshire'" an£t South Wales .... Lancashire ....

miners

These

to

TABLE IV.

1900-02.

the

instance

measles,

to exert a favour-

PHTHISIS MINERS.

Coal-field.

among

cough,

I wish to point

to d u s t t h e

dust

whooping

Total No. of deaths,

is t h i s a c c e p t e d

TABLE

Whffe

in this

conditions.

dust

silicosis. MORTALITY

to c l i m a t i c

ascribed

from person to person.

but

coal

consider

moment

So much been

coal-

which occur on the

to t h e f a c t t h a t c o a l d u s t a p p e a r s able influence.

that

influence

I

v a r i a t i o n s in p h t h i s i s m o r t a l i t y For

from

alongside

only in this country,

phthisis.

different fields.

rates

by coal miners on every

field

of

diseases,

This view of the case would place adult phthisis

Cocd-mining. - - T h e

a

respiratory

work far apart.

of g a n i s t e r b r i c k s .

prevalence

99

exposure

of p h t h i s i s i n t w o

i n d u s t r i e s (i.) c o a l - m i n i n g , a n d (ii.) t h e m a n u f a c t u r e

exerts

HEALTtt.

exerting

is w o r t h

a favourable

close attention.

of dust were condemned

attention was drawn

by me

to light a similarly low

to t h e p a r t i c u l a r l y

furnace

a n d to t h e f a c t t h a t s o f a r a s p h t h i s i s is c o n c e r n e d ,

associated with an abnormally

men

which

high mortality

is

from

no other

pernicious nature of silica dust,

dust appeared

to b e

sb~ilz:!v

ii@'ri,t:~'.

IV[ARCH,

PUBLIC HEALTH.

ioo

through

fields the i n c i d e n c e of p h t h i s i s ( a l t h o u g h a b s o l u t e l y

r e c o g n i s i n g that s o m e dusts of o r g a n i c origin m a y

low), w h e n c o m p a r e d with t h a t of o t h e r fields, is

h a v e a f a v o u r a b l e influence.

h i g h (see Table 3).

A further advance

is n o w

being

made

T h e figures h e r e g i v e n also s h o w t h a t on these

INORGANIC D U S T . T h i s g r o u p also h a s t w o s u b - ~ v i s i o n s : (i.) i n e r t

fields the i n c i d e n c e of p n e u m o n i a and b r o n c h i t i s is TABLE V.

Inert Dusts.--The m a j o r i t y of i n o r g a n i c dusts, although

m o s t of t h e m u n d o u b t e d l y p r e d i s p o s e to

such r e s p i r a t o r y diseases as a s t h m a , p n e u m o n i a and b r o n c h i t i s , are inert so far as p h t h i s i s is c o n c e r n e d .

MORTALITY FROM BRONCHITIS AMONG COAL MINERS. Total No. of deaths.

Coal-field.

D u s t s of l i m e s t o n e , o x i d e of iron, p l a s t e r of P a r i s , aIabaster,

and

plastic

clays

are

examples

of

i n o r g a n i c dusts w h i c h a p p e a r to e x e r c i s e no influence upon a n y f o r m of p u l m o n a r y disease. B a s i c slag, e m e r y and glass a r e i n o r g a n i c dusts

which predispose

examples

of

to p n e u m o n i a

a n d b r o n c h i t i s , b u t n o t to phthisis.

HarmCul Dusts.---This group, so far as e v i d e n c e goes to-day, is e n t i r e l y m a d e u p of the v a r i o u s f o r m s of silica dust.

We

do n o t k n o w of

the

poses to tuberculosis, r e s u l t i n g f r o m d u s t i n h a l a t i o n , a m o n g a n y g r o u p of p e r s o n s e x c e p t t h o s e e x p o s e d to the inhalation of silica d u s t (8). T h e silica m u s t be f r e e in the f o r m of flint, q u a r t z , or q u a r t z i t e , f o r m of a salt, i.e., as a silicate.

G e o l o g i c a l l y I should r e m i n d you t h a t silica is considered a n acid.

C h e m i c a l l y , it b e l o n g s to t h e

s a m e g r o u p as c a r b o n , and it p o s s e s s e s a s i m i l a r

Comparative Mortality Figure.

Median age at death.

1900-02 Durham and Northumberland .. , Nottinghamshire and Derbyshire . . . . Yorkshire .... Staffordshire . . . . Monmouthshire and South Wales . . . . Lancashire ....

41

..

64 to 65

170 221 252

49 67 104

.. ,, ..

67 to 68 62 to 63 64 to 65

435 296

104 1113

.. ..

6l to

58

..

66 to 67

,.

256

Occupied and R e t i r e d Males . . . . . . 40,292

o c c u r r e n c e of that f o r m of fibrosis w h i c h predis-

and n o t in the

(See Tables 4 and 5).

m u c h a b o v e the n o r m a l .

dusts, (if.) i n j u r i o u s dusts.

..

62 58 to 59

1910-12.

Nottinghamshire .. Durham and Nortimmberland .... Derbyshire .... Yorkshire .... Staffordshive Monmouthshire" " an'ci South Wales . . . . Lancashire ....

87

..

25

..

71

4t4 144 .'3130 244

.. .. .. ..

33 39 45 61

.. .. .. ..

67 to 68 67to68 66 to 67 67 to 68

538 462

.. ..

66 88

.. ..

64 to65 64 to 65

Occupied and Retired Males . . . . . . 37,648

..

:f8

..

67 to 68

c a p a c i t y to c a r b o n for f o r m i n g colloidal c o m p o u n d s . T h e case, so far then, is t h a t t h e r e are (c~) s o m e d u s t s of o r g a n i c o r i g i n w h i c h e x e r t a f a v o u r a b l e i n f l u e n c e u p o n the i n c i d e n c e of phthisis, (b) s o m e dusts,

mostly inorganic, which

are

neutral, and

(c) others, c o m p o s e d of silica, w h i c h are d e f i n i t e l y harmful. T h e n e x t q u e s t i o n is to c o n s i d e r w h a t o c c u r s when

harmful

and favourable

dusts

are mixed.

I h a v e a l r e a d y a l l u d e d to t w o i n s t a n c e s , a n d m u s t

Coal M i n i n g . - - C o a l m i n e r s a r e e x p o s e d not m e r e l y to coal dust, b u t to d u s t a r i s i n g f r o m the These rocks

u n d o u b t e d l y c o n t a i n m u c h f r e e silica ; yet t h e coat m i n e r does n o t s u c c u m b

to t u b e r c u l a r silicosis.

M i n e dust, n e v e r t h e l e s s , does not affect all m i n e r s alike.

S o m e m e n , the colliers, get coal, while e t h e r s

rip a w a y t h e r o c k ; t h e l a t t e r get m o r e r o c k dust. O n s o m e coal fields, of w h i c h

L a n c a s h i r e is a n

is a f u r t h e r

y o u n g e r are its v i c t i m s .

point : - - t h e d a t a p r e s e n t e d T h i s v a r y i n g m e d i a n age

at d e a t h has its i m p o r t a n c e in v i e w of D r . J o h n Brownlee's conclusion

(9) t h a t t h e r e a r e different

t y p e s of phthisis, o n e of w h i c h he calls " old age " phthisis.

C o n c e r n i n g this t y p e he w r i t e s : " T h e

o n l y a s s o c i a t i o n w h i c h has b e e n m a d e out q u i t e defin!tely and b e y o n d d i s p u t e is that it is e s p e c i a l l y common

n o w d e a l with t h e m in g r e a t e r detail.

rocks a m o n g w h i c h coal is found.

There

i n d i c a t e t h a t the less the a m o u n t of phthisis, the

among

m i n e r s , coal, iron, lead, etc., a n d

also a m o n g the w o r k e r s in tile W e l s h slate q u a r r i e s . The cause

of this a s s o c i a t i o n is at p r e s e n t q u i t e

unknown."

T h e p r e s e n c e of an u n d u e amoun~c of

this t y p e of p h t h i s i s in a n y g r o u p of m i n e r s w o u l d raise tile m e d i a n a g e at d e a t h f r o m phthisis a m o n g t h e group. Reference

has

already

been

made

to

the

i m p o r t a n c e s t a t i s t i c a l l y of the p r e v a l e n c e of o t h e r respiratory

diseases

such

as

preumonia

and

i n s t a n c e , o w i n g to t h e lie of t h e coal, m o r e r o c k

b r o n c h i t i s , w h e n t h e r e l a t i o n to p h t h i s i s of d u s t

r i p p i n g is d o n e t h a n

inhalation

on others.

O n t h e s e coal

is u n d e r c o n s i d e r a t i o n .

The incidence

PUBLIC

I9~I.

of these diseases among coal miners is important. N o suggestion has been p u t forward that coal dust in a n y w a y checks the incidence of these diseases. P n e u m o n i a among Coal M i n e r s . - - T h e m o r t a l i t y from p n e u m o n i a on the different fields is found to vary within wider limits than that of phthisis. Moreover, for certain fields it exceeds the s t a n d a r d given for occupied and retired males, i n both decennial periods the s a m e three fields are at the bottom of the list, with L a n c a s h i r e m a i n t a i n i n g its u n e n v i a b l e last place. T h e m i n e r on the L a n c a s h i r e field in 1900-02 stood among the twenty-six occupational groups with the highest m o r t a l i t y from p n e u m o n i a ; a position shared in 1890-02 by the miner of M o n m o u t h s h i r e and South YVales. Derbyshire, Nottinghamshire, Durham and N o r t h u m b e r l a n d are at the top for both decennial periods, and they a p p e a r e d in 1900-02 a m o n g the twenty-seven occupations with the lowest m o r t a l i t y from pneumonia. In the case of this disease (in contradistinction to phthisis) the tendency is for the median age at death to be lower than n o r m a l in those fields where the m o r t a l i t y is high. I f we a c c e p t that the disease is influenced b y dust inhalation lowering the p u l m o n a r y resistence this tendency is what might be expected.

Bronchitis among Coal M i n e r s . - - T h e m o r t a l i t y from bronchitis on the different fields varies within wider limits than in the case of pneumonia, H e r e again the s t a n d a r d is sometimes exceeded and to a greater e x t e n t mad by more fields. T h e same three fields, found at the bottom for the pneumonia mortality, are again at the bottom for both decennial p e r i o d s ; a n d again L a n c a s h i r e is easily last. N o t t i n g h a m s h i r e , Derbyshire, D u r h a m and N o r t h umberland, are again found top in both periods. T h e r e is the same tendency as in the case of p n e u m o n i a for the median age at death to be lower than n o r m a l in those fields where the m o r t a l i t y is higher.

HEALTH.

T h e position a p p e a r s to be as follows : - - O n some coalfields there is exposure to injurious dust containing silica, which causes bronchitis and p n e u m o n i a and would cause an excess of phthisis were it not for the c o a l - d u s t ; but the effect of silica in causing phthisis is in some w a y interfered with b y coal-dust. On other coalfields where the exposure to silica dust is less, bronchitis and p n e u m o n i a are less prevMent, and the favourable influence of coal-dust is more clearly manifested. Ganister bricks.--This industry (10) is even more interesting. Good ganister contains u p w a r d s of 98 per cent. of silica ; it is a v a l u a b l e refractory material, used for the m a n u f a c t u r e of bricks, employed for lining steel furnaces. L i m e is used to hold the material together in m a k i n g first grade bricks. T h e men who m a k e these bricks are exposed to silica dust and suffer a h e a v y mortality from tubercular silicosis (see Table 6). T h e d a t a given in T a b l e 6 express this mortality as a p e r c e n t a g e , 76 per cent. of deaths from All Causes. In one district, w h e r e a mortality per 1,000 living could be roughly calculated for the ganister brick makers, it w a s found to be somewhere a b o u t 37 per 1,000 per annum, as contrasted with 1"3 for the town where they worked, 1"0 for m a k e r s of ordinary house b r i c k s and plain tiles, and 2"0 for All Males. I n this district the deaths from other respiratory diseases a m o n g the silica-brick m a k e r s a m o u n t e d to somewhere a b o u t 16 per 1,000 per a n n u m as contrasted with 2"1 for o r d i n a r y brick m a k e r s and 2"8 for All Males. P r o b a b l y the percentage of deaths due to other respiratory diseases stated in T a b l e 6 for first grade silica-brick m a k e r s u n d e r e s t i m a t e s the p r e v a l e n c e of this cause of death, owing to the large percentage of deaths due to phthisis overwhehning the percentages due to other causes. P o o r ganister contains some fireclay in addition to some 87 per cent. of silica; this clay is used to hold the material together for m a k i n g a second

TABLE VI. GANISTER-BRICKMAKERS.--DEATHS

N umber. Cause of death.

Iot

AT A L L

AGES,

Median age at death.

Per Cent.

Makers of silica bricks. / All -: . . . . . . . . . . I males. First grade.[ Second grade. First grade. Second grade.[ Makers of silica bricks.

t/-S 8

Makers of silica bricks.

First

39 to 40 103 . 2 PhthiMs . . . . Other respiratory 40 10.4 27.2 t 17"8 diseases . . . . 14 I 12 40to41 100-0 t00'0 / IO(LO 135 44 MI Causes . . . . Constructedfronl Repocton tile Manufacture of Silica Bricks. W . S . Smithand

tSeco,d gr2de [ /

/ |

All Males.

...

38-39

... 48 to 49

60-61 57-58

E. L Collis.

I02

PUBLIC

HEALTH.

quality of bricks. T h e men who m a k e these bricks, although exposed to dust like the other men, have not been found to .~uffer from tubercular " silicosis. F i r e c l a y , which I would r e m i n d you is a coal m e a s u r e rock found beneath the coal, in some w a y seems to counteract the influence of silica. T h e position here s e e m s to be s o m e w h a t as follows :--A1J acid material, silica, when it reaches the lungs in fine particles sets up a reaction which results in the formation of fibrous tissue, now k n o w n pathologically as silicosis. L u n g s so d a m a g e d fall a ready p r e y to the t u b e r c l e bacillus. Silicon like carbon forms colloidal compounds. Silica in fine particles can also do this. B u t the p o w e r of silicon compounds to become colloidal is interfered with by the presence of acids. F i r e c l a y s , which are silicates mixed with some free silica, when first brought to the surface will not work s a t i s f a c t o r i l y ; they are not sufficiently plastic ; the custom in the trade is to leave them to " w e a t h e r " for years, after which t h e y become more plastic, i.e., m o r e colloidal. To-day, " w e a t h e r i n g " is thought to consist in the washing a w a y o f c e r t a i n o r g a n i c acids,which h a v e b e e n carried down into these clays from the o v e r l y i n g coal measures. After " weathering," fireclay becomes colloidal; a n d potters' clay, which is p r e p a r e d by carefully washing, so that even if it originally held a n y organic acids, it is freed from them, exerts no inhibitory effect upon the action of free silica. SPECULATION.

T h e suggestion may, therefore, be t e n t a t i v e l y m a d e that when silica dust is inhaled with raw fireclay dust, the organic acids in the latter prevent the silica particles from b e c o m m i n g colloidal before they are removed by plagocytic action. T h e next suggestion is that fine silica dust not so p r e v e n t e d from becoming colloidal, m a y enter into the colloidal carbon compound, the protoplasmic tissue of the lungs, with the formation of a silica-carbon compound, which we know as silicotic fibrosis; and that this tissue of low metabolic activity, falls an easy p r e y to tubercle bacilli. You will recall how, in the first chapter of his text book on l?hysiological C h e m i s t r y , t3m~ge wrote : - " Silicic acid and carbonic acid are ' the two g r e a t powers in the construction of the earth,' and are a l w a y s at w a r with each other, with a l t e r n a t e v i c t o r y and defeat on each side." In the cold and in the presence of water, carbonic acid is in the a s c e n d e n t ; but at higher tempera-

MARCH,

tures silicic acid is the more powerful. This chemical rivalry in the external world surely does not cease within the living body where chemical processes take place at lower t e m p e r a t u r e s than are needed in the l a b o r a t o r y ; theory rather suggests that when silica is introduced into the body some definite chemical reaction should occur. T h i s theoretical reaction m a y be likened to that proposed by Lt ewelly n (12) i n relation to the formation of gout tophi, which he holds is determined by the precipitation of crystalloids held in concentration at the surface of colloid elements ; these elements in their turn acting as d e t e r m i n a n t s of precipitation when crystalloids are in excess. I n this instance inorganic b i u r a t e of sodium is deposited m an organic f r a m e w o r k , b u t in the case of silicosis the theory p o s t u l a t e s the formation of carbon-silicon tissue of low vitality. I would remind you when ~enturing on this suggestion that carbon and silicon are both tetravalent elements belonging to the s a m e group ; and chemistry teaches that when two such elements are in solution together they a l w a y s share in the chemical combination present. T h e r e is, therefore, no chemical objection to this theory. T h o s e of you who a r e a c q u a i n t e d with the interesting work done by H a l d a n e and Mavrogordato wilt recognise that the theory above outlined, while it is in no way in opposition to the adsorption theory put f o r w a r d by them, a t t e m p t s an explanaton of the formation of fibrous silicosis. W e h a v e to face in silicosis the formation of tissue as new and as out of place as a gouty tophus. T h e most recent work on gout, a l r e a d y alluded to, demands the interposition of one or more infective micro-organisms to d e t e r m i n e the precipitation of biurate of sodium. O n l y lately W ' a t k i n s - P i t c h f o r d in South A f r i c a has pointed out t h a t latent silicosis is precipitated by t u b e r c u l a r infection (13). P e r s o n a l l y I have long leaned to the view that the explanation ot silicosis wilt be found to be intrinsically a bio-chemical one. T h e mechanical explanation that it d e p e n d s on the sharpness and hardness of the particles does not seem to me to suffice. P a r t i c l e s of e m e r y and of glass are as sharp and as h a r d as those of silica, y e t those exposed to their inhalation while suffering in excess from bronchitis a n d pneumonia, do not suffer from any pronounced excess of phthisis, nor have their lungs been found to exhibit either the clinical signs of fibrosis or the mottling typical of fibrous silicosis

I92I.

PUBLIC

when submitted to radiography. F u r t h e r the mechanical explanation loses sight of the minute-

lO3

HEALTH.

8 per cent. phosphorus, but attention m a y be drawn

ness of the particles concerned and their slow rate

to the presence of phosphorus in most specimens of silica. T h e amount, though not large, has been

of m o v e m e n t in the alveolar air which must entirely neutralise a n y possible abrasive properties. These

enough to give rise to poisoning when phosphoretted hydrogen is evolved from ferro-silicon. These

particles can only be imagined as just floating into the atveoli on deep inspiration, and as being moved

points

from thence either by phagocytosis or by the gentle pressure of respiratory movements. To-day the theory put forward may be little more than a speculation. Nevertheless it suggests interesting problems for bio-chemical investigation. P r o b a b l y the chain which determines tuberculosis, like the chain of other pathological disturbances, has at least three links.

T h e first is the link of

latent capacity, inherited predisposition if you will - - t h e capacity living matter possesses of having its normal metabolic changes d i s t u r b e d - - a capacity which varies with races, individuals and occasions. T h e second link represents the conversion of this latent capacity into a real capacity, whether through t r a u m a or other interferences with normal metabolism.

T h e third represents infection which

in the case of tuberculosis is accepted to be a particular bacillus, although, in the case of other disease entities, such as pneumonia, one or more micro-organisms, non-pathogenic possibly in the absence of the second link, m a y by the precipitating cause.

There

is

to day

but

little

probability of

establishing control of the first link which represents e u g e n i c s ; or of the third link which would mean eradication of the bacillus. The second link remains, the link of b i o - c h e m i s t r y ; here the p h e n o m e n a associated with silicosis may give help. T h e first problem is to ascertain what influence fine silica particles alone exert on the t i s s u e s ; and second to ascertain whether this influence is affected by the presence of fireclay. T h e n , starting backwards from the last link, to ascertain what influence coal dust exerts on the tubercle bacillus ; a n d what is the relation between fibrous tissue and the tubercle bacillus. T r a u m a is accepted to be a starting point for fibrous tissue and for localising tuberculosis,yet the relation of the bacillus to fibrous tissue has not, so far as I a m aware, been worked out. Certainly the ash of silicotic fibrous tissue has been found in South Africa to contain a fair a m o u n t of phosphorus as well as of silica. T h e origin of this phosphorus may be nuclein, which contains 7 to

gain

interest

from consideration of the

chemical composition of the ash of tubercle bacillus which has been stated (14) to be : Per Cent. Sodium ...... 13"62 ... 9"18 Potassium ...... Calcium ......

6"35 12"64

... ...

26"55 2"17

Magnesium Silica ......

...

11"55 0"57

... ...

3"22 0"19

Phosphoric acid

..

55.23

...

51.15

?

...

6"60

Chlorine

......

Sulphuric acid ... ? ... 0'84 I should, however, point out that knowledge concerning the chemical composition of the ash of micro-organisms is not extensive, a n d considerable search has failed to discover any other analyses for comparison with these for the tubercle bacillus. E v e n these are too diverse for reliance to be placed on them.

Further, I can find no chemical

analyses of ordinary fibrous tissue. T h e utmost for the m o m e n t which can be said is that silicotic fibrous tissue seems to provide the food required by the bacillus. E v e n should further investigation show some affinity between the tubercle bacillus and fibrous tissue, still no explanation is afforded of why the coal m i n e r experiences an u n u s u a l l y low mortality from phthisis. Here for the present I am content to recognise the fact and to avoid further speculation. BIBLIOGRAPHY. i. Brend, W. A. " The Mortalities of 13irth Infancy and Childhood." Medical Research Committee. S2becial Re2bort, Series No. 10, 1917. 2, "The Boot and Shoe Industry," S2hecial Report Series, No. 1, Medical Research Committee, 1915. 3. Collis, E. L. "The House in Relation to Tuberculosis, considered with regard to the conditions of Factory Life." Trans. S i x t h A ~ n . Co~*fer. N a t . Assoc. Prey. Censure. Leeds. 1914. 4. Collis, E. L, "The Effect of Occupation upon the Incidence of Pulmonary Tuberculosis." Tubercle. 1919. 5. Collis, E, L. "The Effects of Dust in Producing Diseases of the Lungs.*' Prov. X V I I . I~ter~atiomd Congress of Medicine, 1913. 6. Vernon, H.M. " Fatigue and Efficiency in the Iron and Steel Industry." Industri*rllVatigueResearchBoard. i~@ort No. 5. H.M. Stationery Office, 1920. 7. Collis, E. L. I n d u s t r i a l Pneumonoconioses, Milroy Lectures (1915). H.M. Stationery Office, 1919.

PUBL,IC HEA LTH.

~o4

8. Second Report of Royal Commission on Metall retorts Mi~es and Qu~rr;qes. pp. 133-135, (Cd. 7476). 1914 9. I3rowniee, J. " An Investigation into the Epidemiology of Phthisis in Great Britain and Ireland." Medical Research Com~lHtlee, Re~)ort No. 18, 1918. Re~ort No. 46, 1920. H . M . Stationery Offme. 10. Smith, W. S. and Collis, E . L . " Manulacture of Silica Bricks." Home Office Re~ort. H.M, Stationery Office. 1917. 11. Bunge, G, t~hysiolo~,ic~rl a~zd Pathologiccd ChemistJ W. Translated. Kegan, Paul, Trench, Trubner and Co. 1902. 12. Lleweltyn, L . J . Go~t. William tteinemann, 1920. ~3. A.mu~ag Report of Mi~ters' P h t h i s i s Bo¢~rd. Union of South Africa, Capetown. 1920. 14. Cahnette, A. L'Ii~fection Bc~cil&dre et lg Tuberculose. Masson et Cie, Paris. 1920.

RAT R E P R E S S I O N IN T H E CITY OF MANCHESTER.* BY

M.D., D.P.H., Assistant to the Medical Officer of Health, Manchester. W.

ALLAN Y O U N G , D . S . O . ,

The reason this subject was selected was that, apart from the stress laid upon this work by the Ministry of Agriculture and the impetus given to it by recent Rat Weeks, it was thought that we should be able to learn from the discussion something of the different methods adopted and of the work done in different locaiittes, and so be of assistance to one another. Occasional complaints of damage caused by rats have been received and dealt with by the Public Health Department in previous years, but no special effort was made to deal with the rat problem until the responsibility of carrying out the duties o.f the Rats Order of I918 was placed on Local Authorities by the further Order known as " T h e Local Authorities (Food Control) Order (No. 5), I 9 1 8 " " The administration of the Order in Manchester was at fi'rst undertaken by .the Local Foodstuffs Committee, who, after making certain investigations as to the nature and extent of rat infestation in the city, passed a resolution on June 25th, 1919, suggesting that the work should be carried out by the Public Health Committee. This was arranged in September, i919, a~ld the work has since been carried out under the direction of the Medical Officer of Health. * Paper read at a Meeting of ~he N.KV. Branch held in Manchester, on Friday, November 12th, 1920.

MARCH

Preparations were made for the National Rat Week, which was held in October, I9I 9. Handbills, large posters, and press notices were issued, impressing upon owners and occupiers of infested premises the necessity for taking concerted action for the destruction of rats. infested premises were visited by Sanitary inspectors, pamphlets were lef.t dealing with methods of destruction which could be adopted and subsequent visits were paid to ascertain results. From the information obtained as a result of the above measures, it was evident that certain parts of Manchester were badly infested, and it was decided that for a successful and continued campaign against rats it would be necessary to appoint a whole time Rat Executive Officer. This ONcer was appointed in March, t92o. Rat weeks were held in Manchester in January and March this year. These rat weeks were a means of stirring up the public to the necessity for concerted action, and the complaints, which came in as a result of the advertisements, afforded useful information as to the parts of the city which were infested. The type of rat found in the city is the brown rat (rattus norvegicus). It is sometimes called the sewer rat, and is found in sewers, drains, basements of buildings, stables, and in burrows on canal and river banks. It is a great burrower, and very often finds entrance to buildings through defects in the drainage system. Certain vacant piots of land adjoining warehouses in the city have been found to harbour many rats; their runs have been traced to defective basement windows, doors and ventilators. The black rat (rattus rattus) is found in small numbers in the docks at Manchester and frequently in ships in the port. They are also stated to have been found in one or two warehouses in the Trafford Park District of Stretford. DAMAGE DONE BY

RATS.

No attempt has been made to estimate the amount of damage done by rats in the city, but it must be very great. In addition to the food consumed, the amount which is destroyed is considerable, especially in premises where grain, meat, sugar, etc., is stored in sacks. Recently a large part of a consignment of fresh tomatoes which was stored in the basement of an old building, was destroyed during one