PATHOLOGY. 
or by increasing the fluidity of the alimentary mafs by 
fubftances which are obnoxious; or to induce thefe two 
effe< 5 ts. The firft kind of cathartics probably aft upon 
the mufcular fibres of the inteftines, and the fecond kind 
feem to aft upon the vafcular parts of the inteftines. 
Some cathartics induce an unufual flow of bile into the 
inteftines 5 and in this refpeft they refemble, in their 
modus operandi, the natural ftimulus of the bowels, 
which is the bile. Other cathartics Simulate the exhUlent 
veflels of the inteftinal membranes, and thereby give an 
excefs of fluidity to the volume of their contents : or all 
thefe feveral modes of operation may be united by a fuit- 
able mixture of cathartic medicines. Again, fome ca¬ 
thartics aft efpecially upon the ftomach, and upon the 
upper portions of the inteftinal tube ; and others feem to 
ftimulate particularly the lower and larger inteftines. 
Some operate by emptying the bowels only, without di- 
minilhing the animal vigour ; whilft others fink the 
ftrength of the patient by emptying the Sanguineous fyf- 
tem at the time they hurry away the nutritious aliment.” 
With refpeftto the fubftances capable of producing the 
above-mentioned eftefts; the ingenious authoris inclined 
to think that rhubarb afts almoft exclufively on the fto¬ 
mach and on the large inteftines ; on the former organ 
efpecially when combined with ipecacuanha. Mercurial 
falts (of which thofe in moft common ufe are the blue 
pill and calomel) operate in two ways : by inducing Se¬ 
cretion of bile from the liver, and hence furnilhing the 
bowels with their natural ftimulus to action, or by their 
direft effeft on the coats of the larger inteftines induc¬ 
ing Secretion from the Surfaces of thofe organs. Mr. 
Carlifle fuppofes that the neutral falts aft by exciting 
watery discharges; but the aftion oft thefe fubftances is 
modified by the quantity of fluid in which they are taken, 
and by the previous condition of the alimentary canal; 
for they may be decompofed by the morbid Secretions. 
On this latter account Epfom falts are particularly re¬ 
commended by this author, becaufe, even if decompofed, 
their operation is ftill enfured by the purgative quality 
of their bafe. In regard to the modification produced 
on the aftion of thefe falts by their dilution, it is a cu¬ 
rious remark, that Small quantities of falts diflolved in 
large quantities of water aft with as much force, greater 
certainty, and lefs fubfequent exhauftion, than much 
larger quantities in Smaller menftrua. Caftor oil may be 
confidered as one of thofe rare purgatives which aft ge¬ 
nerally on the inteftinal canal; perhaps by its vifcid ole¬ 
aginous part on the Superior portion of that canal, and by 
its acrimonious refin on the lower bowels. Its refinous 
portion is fuppofed by this author to be particularly ob¬ 
noxious to abforption ; and hence we may infer arifes 
the certainty of its operation. Jalap is one of thofe ca¬ 
thartics which Seems to ftimulate exclufively the peris¬ 
taltic aftion of the bowels, and is therefore of much ufe 
in evacuating them in acute difeafes. Scammony, gam¬ 
boge, and elaterium, aft moftly on the mufcular parts of 
the bowels, and perhaps the nervous; but thefe effefts, 
except in combination with other medicines, are very 
precarious. Aloes of Colocynth are generally fuppofed 
to aft on the lower parts of the inteftines ; but that effeft 
probably arifes rather from the infolution of thofe fub¬ 
ftances until they arrive So far, than from their Specific 
aftion on thofe parts. 
It Seems Scarcely neceffary to remark on the advanta¬ 
geous mode of ufing various forts of purgatives in con¬ 
junction, as that praftice has very generally obtained, 
and is very Successfully applied to all kinds of medici¬ 
nal fubftances. 
Cathartics may be adminiftered in the form of cJyJler ; 
and in many inftances this method has great advantage 
over the ordinary method. The French employ “ lave¬ 
ments" on almoft all occafions. They are chiefly ufeful 
in cafes in which the ftomach is unable to retain, or would 
be injured by, irritating medicines ; as in ga/irids, or 
inflammation of the ftomach, and in febrile complaints 
97 
attended with extreme debility, efpecially in the latter 
ftages ; fince by this mode the contents of the lower parts 
of the inteftines are Simply evacuated, without any fti¬ 
mulus to the Secreting veflels, and with little or no irri¬ 
tation of the fyftem at large. It is alfo to be obferved, 
that confiderably larger doles may be Safely employed in 
this way. It is of advantage to employ fome emollient 
fubftance, combined with the purgative, to defend the 
inteftine in fome meafure againft the acrimony of the me¬ 
dicine. Thus, if the eleftuary of Senna is ufed, it may 
be conveniently rubbed up with a little oil; and the 
whole will then mix uniformly with milk or any other 
liquid. When clyfters are employed as purgatives, it 
muft be remembered that they cannot pafs higher up than 
the valve of the colon, and consequently that they can 
only aft direftly upon the large inteftines. Therefore, 
they can Seldom entirely fupply the place of purgatives 
by the mouth, which pafs through and excite the whole 
inteftinal canal; but they prove moft ufeful auxiliaries, 
particularly in thofe cafes of inteftinal diforder that are 
attended with much vomiting and irritability, where, 
befides emptying the lower bowels, they aft as topical 
fomentations, and very often induce eafe and deep when 
other methods fail. In Such cafes, therefore, they ftiould 
be in pretty large quantity, not very ftimulating, and as 
warm as the patient can bear them. As vermifuges, alfo, 
clyfters have a peculiar and local ufe, where the worms 
are lodged in the lower inteftines ; particularly as very 
highly ftimulating medicines are often required to dif- 
lodge-thefe troublefome animals, which, if given by the 
mouth, might produce a good deal of inconvenience and 
irritation. 
The reader will clearly perceive how insufficient thefe 
observations are, and how much the inveftigation of the 
remote modus operandi of various purges ftill remains a 
defideratum. The fubjeft, however, is confefledly fur- 
rounded with much difficulty ; yet a Series of experiments 
might probably be devifed to throw further light on this 
interefting fubjeft, which ftiould likewife extend to a 
much larger number of cathartics than thofe we have hi¬ 
therto confidered. 
Emetics, or thofe fubftances which operate a rejeftion 
of the contents of the ftomach, are of various kinds. Moft 
of the common poifons are emetics ; and many other fub¬ 
ftances, not deleterious in themfelves, do, when admi¬ 
niftered in exceffive quantities, produce ficknefs. Some 
difputes have been made public concerning the ac¬ 
tion of thefe fubftances; fome phyfiologifts l'uppofing 
that they produced their effeft by ftimulating the fto¬ 
mach to contraftion, others that the abdominal and 
coftal mufcles were the agents concerned, and which 
produced vomiting, the ftomach performing no contrac¬ 
tion. Many experiments have been made on this point; 
and the reiult renders it probable that both the above- 
mentioned powers are concerned in the aft of vomiting, 
and that the cefophageal part of the ftomach is firft afted on. 
The ufe of emetics in what may be termed a reftrained 
or limited degree is frequently attended with the moft 
powerful eftefts. The fenfation of naufea, that l'enfation 
which occurs previous to the aft of vomiting, is in the 
higheft degree debilitating: it reduces the aftion of the 
heart, and is attended with very general fecretion from 
the mucous expanfion of the nofe, eyes, fauces, air-cells, 
and ftomach. Hence dofes of emetics capable of produc¬ 
ing this effeft and no more are ufed in acute difeafes: for 
it is worthy of notice, that beyond the above-mentioned 
point (that of naufea), when vomiting Succeeds, the fyf¬ 
tem appears JlimutatecL, and the cerebral circulation in- 
creafed. So that to produce naufea, and to produce vo¬ 
miting, is a very different matter, and worthy of parti¬ 
cular attention. 
The aftion of the urinary fyftem is increafed by increaf- 
ing the natural quantity of fluids Swallowed, or by the 
ufe of Diuretics. The number of fubftances which 
have been praifed by different writers, as poffefl'edof diu¬ 
retic 
