MATERIA MEDICA. 
165 
mucous coat of the intestines, cause only a slight purging; 
others, that are rarely known to inflame, provoke abundant 
evacuations. 
The effect of purgatives, therefore, cannot be said to be assi¬ 
milated with those of ordinary irritants; the first seem principally 
to exert their influence on the contractility of the intestinal 
canal; the others excite its sensibility. The ordinary irritants 
begin to develope their agency on the stomach; the special ex¬ 
citants, the cathartics, develope them completely in the intestines 
alone. The stomach is not, however, passive under the influ¬ 
ence of the latter; and it even sympathises with the impression 
of those that never entered it, but were administered by injec¬ 
tion, and some of the laxatives act primarily and principally on 
the stomach. 
Soon after the administration of a purgative, animals gene¬ 
rally become depressed and languid, off their feed, yawn (the 
horse), shiver, are evidently nauseated, vomit (the dog). The 
skin is alternately hot and cold; the pulse, at first small, concen¬ 
trated, irregular, sometimes intermittent, acquires force and fre¬ 
quency : eructations follow—sometimes colicky pains—swelling of 
the abdomen ; and, at length, after a variable period of time, 
the alvine dejections appear more or less abundant. 
At the same time, the absorbents take up some of the minuter 
particles of the medicament, and which enter into the circulation, 
and escape through the excretory ducts. They have been de¬ 
tected in the blood ; and the best means of purging a young 
animal is through the medium of the mother. 
Herbivorous animals, on account of their organic structure and 
their peculiar idiosyncracies, are more difficult to purge, and 
take a longer time to effect the purpose than carnivorous ones. 
It is not until twenty-four or thirty-six or forty-eight hours have 
passed, that the former can often be purged; the effect is pro¬ 
duced in the latter by the same medicines in six or eight hours, 
or less. Young animals are much more easily purged than 
old ones. 
The number of the evacuations varies considerably, depending 
on the character of the matters discharged, and their consistence, 
the quantity of intestinal mucus, or the fluids of the absorbent 
vessels with which they may be mixed. To this first series of 
phenomena others succeed not less remarkable. The digestive 
tube, freed from the foreign matter which was accumulated in it, 
and its vital properties newly modified, takes on a new action, 
confined at first to its own proper absorbent system, but soon 
diffused over the whole frame. The respiratory and circulatory 
processes are moderated, and made more regular, whether it be 
