92. After the changes above related, the refuse matter accumulates in the colon, having now acquired that peculiar fetor which distinguishes excrement; it is considerably retarded in this part of its passage by the cells or compartments into which this intestine is divided; at length, however, it enters the rectum, and, by forming a mass of considerable bulk, frequently distends its parietes, and thus creates a sensation of uneasiness, which announces the necessity of relief. If, however, this call be not imperious, and we neglect to obey it, the intestine becoming insensible to the stiniulus of distension, the desire ceases, and may not recur for some time. This effect is greatly modified by the consistence of the fecal matter; if it be soft, or almost liquid, we shall be less able to resist its expulsion. The intervals at which this operation is performed will vary extremely in different individuals: some persons evacuate their faeces twice or thrice a day; others, not more than once in two days; and there are those who, although in perfect health, pass over a week or ten days without any evacuation.

Habit also exerts a wonderful influence in regulating such periods: a person accustomed to the act at a certain hour of the day, will generally feel an inclination at the appointed season.

93. With regard to the relative proportion which the caput mortuum bears to the quantity of food, it is important to observe that different articles of diet yield very different quantities of residual matter, and in selecting a diet for particular forms of disease, this consideration becomes a circumstance of great importance.

94. We have hitherto only considered the digestion of solid aliments: it now becomes necessary that we should investigate the changes which liquids undergo, when introduced into the stomach. The subject teems with many curious physiological facts, and it is one of much importance to the pathologist, as it will enable him to appreciate the utility of liquid diet, and to understand the circumstances which should decide its preference.

95. It was long supposed that liquids, like solids, passed through the pylorus into the small intestine, and were absorbed together with the chyle, or rejected with the excrement. It is not asserted that this never occurs; but it is evident, beyond contradiction, that there exists another passage by which liquids can be conveyed to the circulation: for it has been proved, that if a ligature be applied round the pyloric orifice, in such a manner as to obstruct the passage into the duodenum, the disappearance of the liquid from the cavity of the stomach is not so much as retarded. It is evident, therefore, that there must exist some other passage, although its nature and direction remain a matter of conjecture. I am strongly persuaded, that the vena porta constitutes one of the avenues through which liquids enter the circulation; and, in the Phar-macologia, I have expressed my belief, and supported it by various arguments, that through this channel certain medicinal bodies find their way into the blood.

In order to discover whether drinks are absorbed along with the chyle, M. Majendie made a dog swallow a certain quantity of diluted alcohol during the digestion of his food; in half an hour afterwards the chyle was extracted and examined: it exhibited no trace of spirit; but the blood exhaled a strong odour of it, and by distillation yielded a sensible quantity.

96. When liquids are introduced into the stomach, the changes which they undergo are determined by the nature of their composition.

97. If a liquid, holding nutritive matter in solution, be introduced into the stomach, it is either coagulated by the gastric juice, or its watery part is absorbed, and the solid matter deposited in the stomach; in both cases the product is afterwards chymified in the manner already described. Milk appears to be the only liquid aliment which nature has prepared for our nourishment; but it seems that she has, at the same time, provided an agent for rendering it solid: hence we may conclude that this form is an indispensable condition of bodies which are destined to undergo the processes of chymification and chylification; and that, unless some provision had existed for the removal of aqueous fluid from the stomach, the digestive functions could not have been properly performed. When the broth of meat is introduced into the stomach, the watery part is carried off, and the gelatine, albumen, and fat are then converted into chyme. Wine and fermented liquors undergo a similar change; the alcohol which they contain coagulates a portion of the gastric juices, and this residue, together with the extractive matter, gum, resin, and other principles which the liquid may contain, are then digested, Under certain circumstances, these liquids may observe a different law of decomposition, which will perhaps in some measure explain the different effects which such potations produce: for example, the spirit may undergo a partial change in the stomach, and be even digested with the solid matter, or, on some occasions, converted into an acid by a fermentative process: this will be more likely to occur in vinous liquors, which contain ingredients favourable to the production of such a change; and hence the less permanent and mischievous effects of wines than of spirits1. The liquor termed punch will certainly, cceteris paribus, produce a less intoxicating effect than an equivalent quantity of spirit and water; although it may, at the same time, be more liable to derange the stomach: this may be accounted for, by supposing that a portion of the alcohol is digested by the stomach into an acid, a process which is determined and accelerated by the presence of a fermentable acid like that of lemon, aided, perhaps, by the saccharine matter.

1 Pharmacologia, 8th edit, page 101.