386 
PATHOLOGY. 
irritation of all tliofe parts which hold a fympathy with 
the refpiratory mufcles. Indeed Dr. Bree’s opinion does 
not differ widely from this, as he has allowed that afthma 
frequently has its origin in biiious and gaftric difturbance. 
A further evidence in favour of this notion is, that fome 
afthmatic patients -do not, notwithllanding violent ef¬ 
forts, expectorate ferum or lymph. 
The wheezing noife, and the ftraitnefs and anxiety, 
gave Cullen reafon to fuppofe that a conftrittion of the 
bronchi® took place in afthma. Dr. Bree thinks their 
fymptoms may be more fatisfadtorily traced to detention 
of the ftomach and cefophagus ; when in the former part, 
preventing free infpiration by hindering the defcent of 
the diaphragm ; when in the latter, narrowing the bron¬ 
chi® by preffure. But the mod dyfpeptic patients of 
afthma do not invariably fuffer the above fymptoms in the 
higheft degree. It feems clear therefore, that, though 
contraction of the bronchia is almoft impofiible, a partial 
cloftireof the glottis may occur from fpafm of its muf¬ 
cles, and produce the phenomena in queftion. Indeed 
thefe mufcles are as intimately involved in fympathy 
with the bronchial membrane as the external mufcles of 
refpiration, and confequently are liable like them to have 
this fympathy when kept up for too long a period by ir¬ 
regularity or difturbance in the times of their contrac¬ 
tion and relaxation. We now come to fpeak more par¬ 
ticularly of the two fpecies into which Afthma is divided. 
1. Afthma ficcum, dry, nervous, or convulfive,afthma : 
paroxyfm ludden, violent, and of ftiort duration ; con- 
ItriClion hard, dry, fpafmodic; cough flight; expectora¬ 
tion fcanty,and only appearing towards the clofe of the fir. 
We have before ftated that the convulfive efforts of the 
mufcles of refpiration in this complaint may be called 
into play by irritation of any part of the body the nerves 
of which have influence over thofe mufcles in a ftate of 
health ; fo that dyfpepfia, or difturbance in the liver or in 
the bowels, or even in the uterus, may give rife to diffi¬ 
culty of breathing by impeding the defcent of the dia¬ 
phragm, or by increafing or diminifhing the fympathe- 
tic motion of any of the other refpiratory mufcles ; and, 
as the aClions of the former vifcera are periodical in health 
and in difeafe, the periodic occurrence of nervous irrita¬ 
tion will influence in the fame irregular mode the dyfp- 
ncea, and caufe afthma. 
It is in afthma arifing from thefe abdominal irritations 
that many anomalous fymptoms occur. General ner- 
voufnefs, itching of the Ikin, flufhes of heat, diabetes, 
hyfteria, See. are of no uncommon occurrence; but the 
complaint is too ftrongly diftinguiflied from any of thofe 
complaints to render us liable to miftake in our diagnofis. 
From what has been before ftated, it feems that the 
-caufes of afthma are, nervous irritation of the bron¬ 
chi®, affecting by fympathy the mufcles of the cheft and 
glottis ; or the lame irritation of other nerves fitnilarly 
connected. The fecond caufes are embraced in the ex- 
tenfive views we have taken of dyfpepfia: the former can 
arife only from the peculiar ftate of the bronchial exha- 
lants already mentioned, or the bad ftate of the air in¬ 
haled. 
It remains therefore only to fpeak of aerial irritation. 
In the firft place, it nnift be remarked, that the ftate of 
the bronchial membrane will much alter the nature and 
force of the impreflions it receives from the air. Dr. 
Bree fays, the fenfible membrane of the trachea is na¬ 
turally defended by its lymph from the attack of aerial 
acrimony, as far as the condition of bodies varying in 
fenfibility to external impreflions will admit of this de¬ 
fence. Other things being equal, this guard is fufficient, 
and anfwers the purpofe for which it was defigned. But, 
if the fecretion of lymph from this membrane be defi¬ 
cient, and the abforbing power be aClive, the furface of 
the membrane may be irritated by a thoufand impercep¬ 
tible points which the air conveys in the aft of infpi- 
jation. 
The ftate of air moft congenial to the afthmatic patient 
appears to be that of denfity, a' ftate which more than 
counterbalances the ill effeCts of foreign particles with 
which it is often loaded ; and hence, in the majority of 
cafes, the air in low fituations is more favourable to the 
lungs of afthmatic patients than that of the high lands-. 
It feems moreover, that, even if impurities of the air 
ought to be confidered as the aerial caufe of afthma, thefe 
are more ftrongly applied to the lungs in rare than in 
denfe ftates of the atmofphere, fince in the latter they are 
fufpended at an altitude fuperior to that of the human 
frame. 
Dr. Bree accounts for the good influence of denfe air 
on afthma by ftating, that a certain weight of air is ne- 
ceffary to inflate the lungs fully; and that, the greater 
the force of preffure thus applied, the more perfectly will 
the aerial particles required for the blood be forced 
through the bronchial membrane, or through the collec¬ 
tions of ferum which its tubes may contain. He men¬ 
tions experiments on animals, in which the abforption of 
oxygen was effected with great fpeed when artificial pref- 
fure was applied. He fays, moreover, that, “the ufual 
denfity of the air being lefiened, a certain volume will 
not only poffefs lefs weight, and prefs lefs againfl the 
membrane, but it will alio contain lefs oxygen to enter 
into the new affinity.” 
So much for the ftate of the air as far as regards its 
immediate tranfmiffion to the bronchial membrane. Its 
temperature exerts itfelf with equal power on the Ikin. 
Cold and moifture check cutaneous perfpiration, when 
the body is under their influence : there is therefore ad¬ 
ditional fluid circulating to the pulmonary exhalents, and 
there is lefs expiration of vapour in breathing ; fo that 
we have, in this ftate of the atmofphere, an exciting 
caufe of afthma as frequently as in that of moifture with 
rarity of air. Cold alone will fometimes, but not com¬ 
monly, excite the paroxyfm ; for there may be ftates of 
the atmofphere inducing great torpor on the pulmonary 
exhalents, without the prefence of aqueous vapour, or 
moifture. Thus, the eaft and north-eaft winds would 
exert the beneficial influence which coldnefs, Amply 
united with denfitj' of air, has on refpiration, were it 
not that thefe penetrating winds check cutaneous perfpi¬ 
ration, and thereby induce another caufe of afthma by 
this matter being turned upon the lungs. So on the 
other hand, in fummer and autumn the atmofphere is 
rare, and fo far hoftile to the afthmatic; but, to leffen 
this inconvenience, he enjoys the grateful lenfe of a 
warm Ikin, and general perfpiration, as the circulation 
is determined to the furface during thefe feafons. “ If 
(fays Dr. Bree) it were not for this diverfion in favour 
of the lungs, the patient would perceive much more of 
his complaint than he really does in the warm feafon; 
for many circumftances operate againfl him then which 
do not in winter.” The exhalation from the pulmonary 
veffels, decidedly increafed by exercife or other caufes, 
will oftener be prdfufe in the hot months; and be more 
fuddenly followed by the coldnefs, which is known to 
come upon furfaces in proportion to the evaporation 
made from them, than happens at cold periods of the year. 
This view of the modus operandi of the atmofphere 
is more confonant with legitimate deduction from fafits 
than the old notion that vapours in the air were all the 
offending agents to be looked to, fince it is notorious 
that many afthmatic people live better in the crowded 
and fmoky precin&s of a large city than in the open air 
of the country. Sometimes, indeed, fumes, dull, &c. 
are eafily proved to lead to, or aggravate, an afthma; but 
generally we cannot well confider aerial impreflions to be 
the exciting caufes of the paroxyfms of this malady, fince, 
fuch impreflions beingconflant, the cough and difficulty 
of breathing would be equally fo. We muft therefore 
conclude, that the particles of matter contained in foul 
air accumulate in the bronchia, and affimilate with its fe- 
cretions, until their bulk brings on the dyfpnoeic pa¬ 
roxyfm. 
