the regenerated ferment may act not only upon more of the original proteid, but likewise upon the primary products of its action, thus giving rise eventually to a row of more or less closely related cleavage products. Finally, we can conceive that the enzyme may gradually be affected by the process, that its regeneration may become less complete, and thus digestive power be eventually diminished. Much more might be said in support of the above hypothesis. On the other hand, some objections might be raised against it, but I know of no more reasonable explanation of enzyme action than that here presented, or one which so well accords with all of the known facts concerning the conditions which modify proteolytic action.[48] Thus, the influence of heat, of the products of proteolysis, of acids, alkalies, and various organic and inorganic salts on the action of these digestive enzymes is such as lends favor to the above view rather than opposes it. [48] Compare L. de Jager, Erklärungsversuch über die Wirkungsart der ungeformten Fermente, Virchow’s Archiv, Band 121, p. 182. Also Chandelon: Bulletin de l’Academie Royale de Méd. de Belgique, 1887, 1, p. 289. THE GENERAL NATURE OF PROTEIDS. Proteids are confessedly among the most complex bodies the physiologist has to deal with, while at the same time they are perhaps the most important, not only in view of their wide-spread distribution through animal and vegetable tissues, but because of the prominent part they take in the nutrition of the body. The more our knowledge is broadened concerning these varied substances, the more we are impressed with their complexity, and at the same time with the necessity for a more accurate study of both their composition and constitution. Concerning the latter, full fruition of our hopes is probably in the distant future, but every step of advance in this direction adds greatly to our resources in the interpretation of the varied and complex changes characteristic of proteid metabolism. Every study of proteid decomposition adds something to our store of knowledge, and gives perhaps an added fact available for broadening our deductions.[49] Moreover, the composition and general reactions of the proteids may be investigated with full confidence of obtaining many useful results, which must necessarily be an aid in interpreting the changes accompanying digestive proteolysis. [49] See Drechsel: Der Abbau der Eiweisstoffe. Du Bois Reymond’s Archiv f. Physiol., 1891, p. 248.