least, without farther ill symptoms. Such pains in the bowels resemble those in the bladder, when the detrusor and sphincter are both contracted violently at the same time, by the irritation of a stone. The stomach, the gall-bladder, and rectum, all seem capable of like contractions in muscular fibres, that have opposite actions. The causes of all these spasms and motions are evidently the impressions in the neighbourhood, and their circumstances are, at first sight, agreeable to the theory of these papers.
Eighthly, The glands belonging to the mouth, and alimentary duct, appear to me to be emptied, not only by the compression, which the neighbouring muscles and muscular fibres make upon them, but also by the sensory vibrations which run up their excretory ducts, into the folliculi, and receptacles where there are such, and even into the secretory ducts; by which the peristaltic motion of all these is increased, so as both to receive more freely from the blood during their state of relaxation, and to squeeze more strongly through the excretory ducts during their state of contraction. Thus tobacco, pyrethrum, and other acrids, solicit a profuse discharge from the salival glands, by being barely kept in the mouth, i.e. though the neighbouring muscles do not squeeze the glands by the action of mastication. Thus likewise vomits and purges increase both the secretions of all the glands of the intestines, and those of the liver and pancreas. It may be also, that the vibrations which run up the gall-duct are sometimes so strong as to occasion a spasm there; in which case, if the patient vomit at the same time, a symptomatic and temporary jaundice may follow.
Ninthly, The expulsion of the fæces in new-born children is perfectly automatic, and seems to follow even from very gentle compressions of the abdominal muscles, when the rectum is full, inasmuch as the sphincter ani has in them scarce any force. The same may be said of the expulsion of the urine, the sphincter vesicæ being also very weak in new-born children. To which we may add, that the least irritation from fulness or acrimony in the rectum or bladder throws the abdominal muscles into contraction in young children, both on account of the extreme sensibility and irritability of their whole nervous systems, and because they have, as yet, no associated influences over the muscles of the abdomen, whereby to restrain their contractions.
As the sphincters of the rectum and bladder gain strength, more force is required to expel the fæces and urine. However, it appears, that these muscles usually exhaust themselves, previously to the instant of expulsion, thus giving free scope to their antagonists. For, according to theory, they ought to be contracted sooner and stronger than their antagonists, as being nearer to the seat of irritation.
The actions of vomiting, and expulsion of the fæces, are very nearly related to one another in their automatic state. However, it seems to me, that an irritation in the stomach produces only a
