This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The character of the discharges varies with the mode in which the cathartic acts. Medicines which operate exclusively on the large intestines produce fecal evacuation more or less consistent, Such is the case with aloes and sulphur. Others, which act upon the whole extent of the canal, or particularly on the small intestines, of course evacuate the liquid contents of the upper bowels, and occasion liquid, but still feculent stools. Those which act by increasing serous exhalation, produce thin watery discharges, often very copious, but generally more or less coloured with feculent matter. Bilious stools indicate that the cathartic has operated on the liver. They are sometimes of a bright deep-yellow, sometimes green from the reaction of intestinal acids, and sometimes, when the bile is very concentrated, of a dark-brown approaching to black, but still yellow when in thin layers. irritating cathartics sometimes cause mucous and bloody stools.
Cathartics are usually arranged in three divisions, based upon their difference in activity or energy. The mildest are denominated laxatives; those of considerable energy, but not violent, simply purges, or purgatives; and a third set, which superadd severe irritant properties to their cathartic power, drastic purges, or simply drastics. Though, by varying the dose and mode of combination, much may be done towards obviating these differences of power, yet there is, in this respect, an inherent. and distinctive character in many articles of the class; so that no increase of the dose would give energy to the feeble, and no diminution of it render the violent mild. Thus, there are some laxatives of which no amount that could be used would act energetically on the bowels; and some drastics which, though the purgative effect might be diminished by lowering the dose, yet, when given in quantity sufficient to operate at all, will generally be attended with griping pain, or other sign of irritation.
1. Laxatives not only operate moderately, but with gentleness, that is, without materially irritating the mucous membrane, even, as a general rule, when taken largely. They may occasionally produce griping pains; but these are usually owing to flatulence, consequent upon gaseous matters resulting from fermentation or other decomposition of the laxative itself, as in the case of the laxative fruits, and carbonate of magnesia, or from combinations formed by it in the bowels, as in the case of sulphuretted hydrogen formed from sulphur. The bowels are loosened rather than purged; the evacuations being feculent, and more or less consistent according to the special mode of operation, or the portion of the canal specially affected.
2. Purges may be considered, for convenience of arrangement, as embracing only those cathartics which are capable of operating vigorously on the bowels; but, in whatever quantity taken, are not likely to prove poisonous by inflaming the alimentary mucous membrane. They may exhaust by excessive depletion, but are not dangerously irritant. This statement is not intended to be absolute, but only general. Even inert substances may become dangerous, if given in quantities sufficient, by their mass, or acting mechanically in some other way, to interfere with the functions of the bowels.
3. Drastics, or drastic purges as they are usually called, are characterized by the property of irritating the mucous membrane, and, in overdoses, may produce serious consequences by exciting extensive and severe inflammation in that tissue. Even in their ordinary operation, they not unfrequently cause more or less nausea, faintness, griping pain, and tenesmus; but, when they are taken in excess, these symptoms are much aggravated, severe vomiting and bloody stools occur, the abdomen becomes very painful and tender on pressure, the extremities become cold, the pulse sinks, and life is involved in considerable danger.
The term hydragogue has been applied, as the name itself would indicate, to those cathartics which produce copious watery stools. This property belongs especially to the drastic purges, and it has been not unusual to consider it as embracing these alone; so that, in the mind of not a few, the idea of hydragogue cathartics is associated with something violent and irritating; but the fact is, that the saline purges are not less really hydragogue, and not less, therefore, entitled to the name than the more powerful drastics. When used in this work, or elsewhere by the writer, the term is made to express what it means; simply the property of producing watery evacuations, without reference to mildness or severity of action in other respects.
Griping pain is a very frequent attendant on the operation of cathartics. it depends on spasm of the muscular coat. This may be induced by various causes, and, as stated in the remarks on laxatives, is not always inconsistent with mildness of operation; as, for example, when it depends on the production of flatulence, which, by distending the bowels, calls the muscular coat into irregular action. But it is sometimes caused by high irritation or inflammation of the mucous membrane, which operates in producing it in the same manner as in enteritis and dysentery. Originating in this cause, it is much more serious, and indicates a drastic character in the medicine. There is a third source of griping entirely differing from either of the above. it is the powerful stimulant influence of the cathartic, directed especially to the muscular coat. The griping is an excess of the directly stimulated peristaltic movement. it is in this way that senna produces its characteristic griping effect. The symptom, under these circumstances, indicates no violence of irritation exercised upon the mucous membrane, but simply an energetic direction to the muscular tissue. it may be painful, but is never dangerous, and may in general be easily controlled.
Another difference between cathartics is in their influence upon the system. Some, besides their cathartic effect, and the general depression consequent upon it, have a direct sedative influence on the circulation, and operate as refrigerants. Such are the saline cathartics generally. Others, on the contrary, appear to be tonic or stimulating, increasing the general temperature, and sometimes even the pulse. These are often called warming cathartics. Rhubarb, aloes, and elaterium have more or less of this character. Others, again, seem to have no further operation upon the system than such as results from their action as cathartics. Among these may be ranked castor oil, jalap, scammony, etc. The operation of cathartics is apt to induce thirst; particularly that of the hydragogues. This is owing simply to the depletion they produce from the blood-vessels, a diminution of the contents of which, by a wise provision of nature, induces, probably through the nervous centres, the sensation of thirst, as a means of securing a supply of liquid to replace that which has been lost. The symptom may sometimes also be dependent on the irritation of the mucous membrane, and the arterial excitement which certain cathartics occasionally produce.