Such are the _direct_ conditions requisite for the fulfilment of digestion: but there remain others, of an _indirect_ kind, which also require to be noticed. Of these, a due supply of arterial blood and nervous energy is the most remarkable; but as both produce their effect by modifying the secretions and motions of the stomach, already described as the _direct_ requisites of digestion, it will save a good deal of repetition if, for the present, we take their influence for granted, and reserve their further elucidation till we come to treat of the practical applications of the preceding exposition. * * * * * Having thus obtained a comprehensive view of the agents employed in effecting digestion, and of the changes produced by it on different kinds of food, we find another important subject of investigation, immediately connected with the process, presenting itself--_the comparative digestibility of different kinds of food_. Dr Beaumont did not neglect this branch of the inquiry; but the experiments which he performed for its elucidation are, like those of most of his predecessors, deprived of great part of their value by the vague way in which they seem to have been conducted, and the common omission of all particulars in regard to those conditions which are known to exert a powerful influence on the progress of digestion. The following Table, which I have arranged in a more lucid order than Dr Beaumont has done, exhibits the general results of all the experiments made upon St Martin posterior to 1825; and the average is deduced from those which were performed when the stomach was considered by Dr Beaumont to be in its natural state, and St Martin himself subjected to ordinary exercise. _TABLE shewing the Mean Time of Digestion of the different Articles of Diet._