Similarly, among inorganic compounds, arsenious oxide, arsenic oxide, boracic acid, and potassium bromide38 in small amounts increase the proteolytic power of pepsin in hydrochloric acid solution, while larger quantities check the action of the ferment in proportion to the amounts added. Again, with the enzyme trypsin, similar results with such salts as potassium cyanide, sodium tetraborate, potassium bromide and iodide39 may be quoted as showing not only the sensitiveness of the ferment toward foreign substances, but likewise its peculiar behavior, viz., stimulation in the presence of small amounts and inhibition in the presence of larger quantities.

Furthermore, we have found that even gases, as carbonic acid and hydrogen sulphide, exert a marked retarding influence on the proteid-digesting power of trypsin. Moreover, while it is generally stated that proteolytic and other enzymes are practically indifferent to the presence of chloroform, thymol, and other like substances that quickly interfere with the processes of the so-called organized ferments, pepsin and trypsin certainly do show a certain degree of sensitiveness to chloroform, and indeed even to a current of air passed through their solutions. Thus, very recently, Bertels40 and Dubs41, working under Salkowski’s direction, have called attention to the peculiar behavior of pepsin to chloroform; their results showing, first, that small amounts of this agent tend to increase the proteolytic power of the enzyme, while larger amounts decrease its digestive power. Another interesting point brought out especially by Dub’s experiments is the fact that an impure solution of the ferment, viz., an acid extract, for example, of the mucous membrane of the stomach containing more or less albuminous matter, is far less sensitive to chloroform than an acid solution of the purified ferment, thus showing again the protective influence of proteids and other extraneous matters; the latter guarding the enzyme to a certain extent from both the stimulating and inhibitory action of various agents.