PATHOLOGY. 91 
of another part: fome phyficians admitting the clafs of 
fadts, and-admitting alfo the inference of a relation, be¬ 
lieve that the examples are very rare ; others are inclined 
to think them univerful; aye, and to allow them only 
one tendency, although they might tend to fifty, or five 
hundred, different eft'e&s. It will appear from this ac¬ 
count that the exiftence of related difeafe has been long 
known, that the knowledge of it has become popular, 
and confequently there is no novelty in the ftatement of 
the fadt. If we would improve our knowledge with ret 
pedt to fuch difeafes, it muff be, not by ignorantly gene¬ 
ralizing a fingle limited clafs, but by a juft analyfis of its 
laws, by an inquiry into its nature, its frequency, and 
by an accurate difcrimination of its inftances. The firft 
fubdivifion which we have propofed of this clafs is that 
of related fecondary difeafe, tending to cure the pri¬ 
mary. 
“ Perhaps the moft unequivocal examples of related 
fecondary difeafe, tending to cure that which occurs in a 
primary feat, are thole of metaftafis. A perfon might 
have pneumonia clearly characterized by its fym'ptoms : 
the fymptoms of this local difeafe on a fudden lhall ceafe, 
and the fubjedt become immediately a fie fled with phre- 
nitis, which lhall be followed by death within eight-and- 
forty hours. Thefe occurrences may be confirmed after 
death by difleftion (quod vidimus teftamur). If we in¬ 
quire into the caufation in this example, there are thofe 
to whom the whole procefs is perfectly clear, who will 
reply, the inflammation left the lungs and went to the 
brain; was it then the fame inflammation? and, if fo, what 
was the objeft of its journey, or why did the inflamma¬ 
tion take it into its head to travel ? To analyze a little 
more curioufly: 
“ Inflammation exifts in the lungs: why does it ceafe 
in the lungs ? either from that progreffive caufation 
(which has been defcribed) taking place in the lungs, or 
from a progreffive caufation taking place elfewhere, by 
which a relation is opened between the feat of fuch pro- 
grefiive change and the properties engaged in the difeafe 
of the lungs, the end of which relation is, that difeafe 
is eftabliflied in a feco.ndary, and ceafes in the primary 
feat. The evidence in this cafe, derived from the order 
of fucceflion, is, that the difeafe in the lungs, being the 
antecedent, is alfo the caufe of the difeafe in the brain 
which fucceeds to it; in other words, the properties con- 
ftituting inflammation of the lungs leave this feat, and 
are transferred to the brain. But, if the pneumonia is the 
antecedent to the phrenitis, what is the antecedent to 
the metaftafis ? or why does a difeafe leave a feat in which 
it is eftabliflied ? The alternatives which muff form the 
anfwer to this queftion are fuggefted above: either a 
change takes place in the properties of the lungs, by 
which they no longer admit the ftate of inflammation, 
which is then affirmed by fome other vifcus, already in a 
predifpofed ftate to take up inflammation upon the cefla- 
tion of it in another feat; or elfe the brain (continuing 
our example) afl'umes a ftate which is fo related with the 
properties engaged in the inflammation of the lungs, as 
to produce a ceflation of the inflammatory condition in 
this feat. From this view it is obvious, that the fenfible 
fucceflion is inadequate to determine the caufation; for 
the brain may be the firft to afi'ume a change, by which 
it cures the difeafe in the lungs; or the difeafe may 
ceafe in the lungs, from caufation proceeding in this 
feat, and be aflumed by the brain, or any other feat 
which is predifpofed to this refult, under the relations 
which obtain upon the ceflation of a difeafe in a feat 
which it had hitherto occupied. 
“The alternatives here fuggefted muft obtain in every 
cafe in which the primary ceafes upon the occurrence of 
the fecondary difeafe, but they do net neceflarily obtain 
in all cafes of related difeafe : thus we fay dentition dif- 
orders the bowels ; this is a cafe of Ample fucceflion, 
which, by analogies before explained, we infer to be 
alfo one of caufation. If, upon the occurrence of dil- 
Vol. XIX. No. 1289. 
order of the bowels, the procefs of dentition w-ere fuf- 
pended, we fliould then have to determine whether the 
change preparatory to the metaftafis took place in the 
bowels or in the maxillary nerves. The progrefs of con- 
fumption might be fufpended upon the occurrence of 
pregnancy; here confumption, as a related ftate, preceded 
pregnancy, yet we know, as the caule in this inftance is 
palpable, that the feat of that change which produced the 
mataftafis was the uterus, or fecondary related feat. 
Thus alfo the catamenia may be checked by an expofure 
to cold, which will produce rheumatifm; the change 
preparatory to, or caufative of, the metaftafis, is here 
alfo in the fecondary feat. From thefe and many fimilar 
examples, we may perhaps conclude very generally, 
that the primary difeafe in metaftafis does not produce 
the fecondary, but that the metaftafis itfelf is determined 
by a change which takes place in the fecondary feat. 
“ Related difeafe, according to our reduced divifiori, 
is of two kinds : ift, as when a primary difeafe ceafes 
upon the occurrence of a fecondary; and, 2d, as wdien 
a fecondary merely fucceeds to a primary dileafe. The 
former inftances have been exprefled by the word metafld- 
fis, which implies that the difeafe leaves one feat and goes 
to another : this, however, is a conjefture without proof, 
for an inflammation of the eye may be cured by a fponta- 
neous diarrhoea ; if the identical properties of the pri¬ 
mary difeafe went to the leat of the fecondary, thefe 
properties, being thofe of inflammation, fliould produce 
inflammation of the bowels rather than a diarrhoea, 
which rarely occurs in inflammation of the bowels. If 
the identical difeafe of a primary is in metaftafis tranf- 
ferred to a fecondary feat, as the charaEter of the fecondary 
is commonly very different from that of the primary difeafe , 
it is necelfary to infer that the identical nature of the 
primary difeafe is liable to be modified by peculiarities 
which belong to the fecondary feat. 
“ This firft clafs of related difeafe, then, viz. that in 
which a primary ceafes upon theoccurrence of a fecondary 
difeafe, may be called JubJlitution of difeafe; which 
merely exprefles the fadt that one difeafe has taken place, 
while another has ceafed : the word ‘ vicarious,’ which is 
familiar in medicine, exprefles the fame thing. The fe- 
cond clafs of related dileafe, viz. that in which the pri¬ 
mary does not ceafe upon the occurrence of the fecondary, 
may be called related extenfion of difeafe (the caufative 
relation being in both cafes aflumed upon the grounds 
before ftated). 
“ The examples of fubftituted difeafe are very nume¬ 
rous; and it is upon this experience of their frequency 
that the relation of caufe and eft'edt in fome or other of 
its modes comes to be inferred to fubfift very generally 
between them. We cannot, however, upon this point 
compel belief. Although the examples of fubftituted 
difeafe are very numerous, they are not fufficiently regu¬ 
lar to admit a claffification of thofe primary difeafes 
which are likely to be cured (to beg an expreffion) by 
the occurrence of fecondary ones. We can rarely, 
(owing to this irregularity) perhaps we can in no cafe, an¬ 
ticipate. the cure of a primary difeafe by a fecondary one; 
that is, we cannot pronounce that a certain fecondary 
difeafe will fucceed to the primary, and that the latter 
will then ceafe. We more frequently expedl the cef- 
Jation of a primary difeafe, when the fymptoms of a fe¬ 
condary one, of the tendency of which we have had ex¬ 
perience, do actually appear, than we anticipate a fubfti- 
tution of difeafe, while the exifting fymptoms occupy 
exclufively the primary feat. There is, however, an ex¬ 
ception to this remark, when the fame fecondary has been 
fubftituted for the fame primary dileafe, in one or more 
inftances.” Pring, ch. v. 
Difrnifling the confideration of thefe abftrufe and ob- 
feure fubjedts, we next proceed to confider the fymptoms 
of difeafes ; a fubjedl of the firft moment, and one w hich 
deferves the moft unremitting obfervation; for, though 
the caufe of the difeafe may be obfeure, and though its 
B b laws 
