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PRE FACE.

A portion of the contents of this volume formed the substance of a part of my “Gulstonian Lectures,' delivered at the Royal College of Physicians in 1862. The view that will be found to be advanced in explanation of the manner in which the stomach escapes undergoing self-digestion during life was first alluded to there, and afterwards formed the subject of a paper published in the ‘Philosophical Transactions' for 1863.

At the end of the work reference is made to the employment of artificial digestion as a means of dissolving meat for producing an article of nourishment in which the nitrogenized alimentary principles are in a state ready for absorption.

35, GROSVENOR STREET, GROSVENOR SQUARE;

July, 1867.

GENERAL REMARKS

ON

DIGESTION AND INDIGESTION.

The purport of digestion is the preparation of food for absorption; and its performance as one of the functions of life is called for by the circumstance, that the fluid state forms a necessary condition for the accomplishment of absorption. In organisms belonging to the vegetable kingdom an absence of a digestive system is to be remarked, because their food, consisting, as it does, of inorganic principles diffused through the atmosphere and dissolved in the moisture percolating the earth, is already in a fit state for absorption by the leaves and roots—the absorbing organs of the plant. In some few animal organisms, also, for a similar reason, there is an absence of digestive apparatus. In the generality of animal beings, however, the food is of a nature to require preparation before it is susceptible of absorption. Hence the demand for digestion as one of the functions of animal life.

Digestion, in a limited sense, may be taken as signifying the phenomena that occur in the stomach and intestine immediately antecedent to absorption ; but looked at comprehensively, the light under which it will be regarded in the following pages, the various

operations accessory to this final act are also included as parts of the

process. Now, the first steps to be taken towards the accomplishment of digestion are PREHENSION and INGESTION. Food must be secured and introduced into the mouth before it can be eaten and digested.

In the cavity of the mouth two operations are performed-MASTICATION and INSALIVATION : the one consisting of a mechanical reduction of the food to a more or less minute state of subdivision; the other, its incorporation with a secretion poured out by a set of glands specially provided for the purpose.

. Thus much accomplished, the food is formed at the back of the mouth into a bolus, and then propelled, by the process of DEGLUTITION, along a canal formed by the pharynx above and gullet below, into the stomach.

Arrived in the stomach, one of the chief acts of the digestive process is performed, viz., CHYMIFICATION, or

The food is brought in contact with a fluid—the product of secretion of the organwhich is endowed with a strikingly energetic solvent power over certain of the alimentary principles. By the agency of this secretion a semifluid material is formed, called chyme, which constitutes the product of gastric digestion.

Having reached the state of chyme, the food passes from the stomach into the small intestine, where it becomes incorporated with various secretions, the general effect of which is to cause the transformation of the watery-looking chyme into a rich cream-like magma. This constitutes CHYLIFICATION or INTESTINAL DIGESTION. The term chylification, however, signifying the production of a chyle-like magma, as representing the

GASTRIC DIGESTION.

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