comes off much more easily, but the manganese dioxide is unaltered at the end of the experiment, and this is quite comparable to what occurs in the case of a ferment. Take another example; in the manufacture of ordinary oil of vitriol, sulphurous acid, atmospheric air, and steam are brought into contact with one another in a large leaden chamber. These three substances alone would suffice to form sulphuric acid (SO2+O+H2O =H2SO), but the action would be a slow one. The combination is hastened by the presence of a small quantity of nitrous acid (NO3). The sulphurous acid (H2SO3) combines with the nitrous acid, and is then decomposed into sulphuric acid (H2SO,) and nitric oxide (N2O2). H2SO3 + N203 = H2SO1 + N202 [sulphurous acid] [nitrous acid] [sulphuric acid] [nitric oxide] The nitric oxide left combines instantly with oxygen, to form nitrous acid again, which in turn undergoes the same decomposition with sulphurous acid. Thus the nitric oxide serves as an oxygen carrier, and as it is continually being recovered, and itself taking no part in the composition of the final product (sulphuric acid), a small quantity will last an indefinite time, and always be ready to perform the same office. Here again it plays the part of a ferment. Take another example, this time from organic chemistry; namely the action of sulphuric acid in the manufacture of ether from alcohol. If one distils together alcohol and sulphuric acid, ether and water will be found in the distillate, and the sulphuric acid apparently unchanged in the retort; and the same quantity of sulphuric acid can be used over and over again, to break up an indefinite quantity of alcohol. Now if the action of the sulphuric acid had not been understood, as it was not until comparatively recent times, the reaction would have been still looked upon as puzzling, and described as catalytic. We do, however, understand how sulphuric acid acts. The first reaction that takes place may be denoted in this way. We start with alcohol and sulphuric acid :— When these come together, the vertical line represents the products of their interaction; they split into HHSO, water ethyl-hydrogen sulphate water, which comes over in the distillate, and ethyl-hydrogen sulphate. The ethyl-hydrogen sulphate reacts with more alcohol, and, the vertical line again indicating the way in which the atoms are rearranged, we have sulphuric acid, again ready to be split up as before, and ether, which distils over. In this reaction the sulphuric acid acts as probably ferments do in fermentation. Apparently they are unchanged at the end of the reaction; probably they have acted in some such way as the nitric oxide or the sulphuric acid do in the examples just given. Probably they play the part of an oxygen carrier, or a water carrier, and then in the later stages of the reaction are deprived of their extra oxygen or water, and thus appear the same as before the reaction began. Lastly, an example may be taken from physiology itself; the example is that of the action of hæmoglobin; it comes to the lungs in the venous blood, is converted there into oxyhæmoglobin, takes the oxygen to the tissues, and returns as it started, in the condition to act over and over again as an oxygen carrier. This action of hæmoglobin is not generally called a ferment action, but it appears to me to be clearly in the same category of phenomena. We do not call it a ferment action, because we understand it; when we attain to a similar accurate understanding of the action of pepsin, and of bacteria, we shall probably cease to call them ferment actions, and reserve that term for what we do not understand as a convenient cloak for ignorance. The action of sulphuric acid in etherification is no longer cloaked under the similar term catalysis. There seems no reason why in the future we may not attain to as accurate knowledge concerning ferment actions as chemists have arrived at in connection with many formerly so-called catalytic phenomena. We have thus a series of occurrences in chemistry, starting with the simple catalytic processes of inorganic chemistry, and ending with the ferment processes of physiological chemistry, probably differing only in the complexity of the substances taking part in them. Ferment activity is a manifestation of protoplasm in a living condition; and I regard it as possible that, by working out ferment actions in the light of the simpler catalytic actions, we shall obtain an insight into the explanation of other still more complex vital actions. A step to the better knowledge of fermenting processes has been made by Hoppe-Seyler, who has pointed out that the oxidation in which the action often apparently consists is not a direct one, but rather of the nature of reduction. 1 The most recent exposition of Hoppe-Seyler's views in this direction will be found in the Zeit. physiol. Chem. x. 36. 2 Thus in the lactic and alcoholic fermentation, and in putrefaction, there is a liberation of hydrogen, and this nascent hydrogen combines with an atom of oxygen from ordinary oxygen (O2) to form water (H2+02=H2O+0). The nascent oxygen (O) thus liberated, oxidises any oxidisable substance present, or it may unite with hydrogen to form water, or oxygen to form ozone (O3). But if on the other hand the nascent hydrogen meets with no free oxygen, it takes the oxygen from organic substances, that is, reduces them. Thus in putrefying liquids, oxidation may be proceeding in the upper portions where there is free access of atmospheric oxygen, and reduction in the lower layers where free oxygen is absent. It is probable that some of the changes occurring during the nutrition of living cells are similar to these fermentations. The nascent hydrogen liberates nascent oxygen, which then oxidises oxidisable material. The following hypothetical formula would represent what occurs; supposing n is oxidisable material, then HH+02+n=H2O+On. THE UNORGANISED FERMENTS These substances can be extracted from the cells in which they occur by water, dilute acids or alkalis, salt solution, or glycerine. They are precipitated from such extracts, or from the secretions in which they occur, by alcohol, or by saturation with ammonium sulphate,' or by lead acetate. The precipitate so obtained is proteid in nature,2 or closely allied to proteid. On drying this precipitate a colourless, tasteless, amorphous powder is obtained. These ferments may be arranged, according to their action, into the following classes :- : 1. Proteolytic those which change proteids into peptones. This is probably a process of hydration, as it can be also brought about by other hydrating agencies, such as boiling with dilute mineral acids, or superheated steam. Examples: pepsin, trypsin, papain. 2. Amylolytic those which change amyloses (starch, glycogen) into sugars. This also is a hydration. Examples: ptyalin, amylopsin, diastase. 3. Steatolytic those which split fats into fatty acids and glycerine. Examples: ferments in pancreatic juice and bile. 1 Krawkoff, J. Russ. Chem. Soc. 1887, p. 387. 2 Elementary analyses have been made of various ferments by Schmidt, Schlossberger, Hüfner, and others. Much the same results have been thereby obtained as in the case of proteids. 1 4. Inversive those which convert cane sugar into glucose. Examples: invertin of intestinal juice, and of yeast cells. 5. Emulsin or synaptase: a ferment which converts glucosides (amygdalin, salicin, &c.) into glucose, and other compounds. Myrosin is a very similar ferment. 6. Coagulative. Examples: fibrin ferment, myosin ferment, rennet, ferment from Withania coagulans which acts like rennet (Lea). A rennet-like ferment is obtained from certain other plants,2 and certain bacteria.3 There are other fermentations, such as the conversion of glucose into mannite, or of glycerine and mannite into alcohol by the action of putrefying nitrogenous organic matter, which have been described, but which are of little importance to the physiologist. The preceding classification is found to be very useful from a physiological standpoint. In many instances the same chemical change, which in all cases appears to be of the nature of hydrolysis, may be effected by the action of ordinary chemical reagents, such as dilute mineral acids, or caustic alkalis. Hoppe-Seyler has accordingly classified ferments from a chemical standpoint as follows: 4 a. Ferments which act like dilute mineral acids at 100° C. : i. Change of starch or glycogen into dextrin and grape sugar.' C2H4000+ 3H2O = C ̧H1O ̧ + 3C,H12O6 [starch] 10 [dextrin] [glucose] ii. Change of cane sugar into dextrose and levulose (inversion). C,,H,O,+H,O=CH,,O,+CH,, [cane sugar] 12 [dextrose] [levulose] iii. Change of various benzol-glucosides into sugar, and simpler benzol-derivatives by the action of emulsin (see p. 109). Example: C,,H,,O,+ H2O = C2H12O+CH, 18 [salicin] 12 [sugar] SCH2OH iv. Decomposition of sulphur-containing glucosides into sugar, sulphuric acid, and oil of mustard, by the action of myrosin." Example: C,,H,,NS,O,,KC,H12O6+HKSO, +C1H ̧NS 10 [potassium [sugar] [hydrogen, [oil of Emulsin was prepared in a very pure condition by Aug. Schmidt (Inaug. Diss. Tübingen, 1871). He found that it had the following percentage composition: C, 48.76; H, 713; N, 14-16; S, 125; O, 28-70. E.g. artichokes, black pepper, &c. See Watts' Dictionary, vol. ii. (1889), p. 545. 3 Warington, Journ. of Chem. Soc. 1888, p. 737. 4 Physiol. Chem. (1881), p. 116. The above formula Hoppe-Seyler's after Musculus. Brown and Morris give a different equation (see p. 104). * In the above equation the process is apparently not one of hydrolysis, but it seems b. Ferments which act like caustic alkalis at a higher temperature. Fermentatire saponification :— i. Decomposition of ethers (fats) into an alcohol (glycerine) and an acid (fatty acid). Example: C,,H10406 + 3H2O = 3(C19H„O2) + C‚¤ ̧ ̧ 57 [tri-olein] 18 ii. Decomposition of amido-compounds with absorption of water. Examples: (1) CON,H,+H,O = (NH,),CO (4) The decomposition of proteids and albuminoids (gelatin, chondrin, &c.) into leucine, tyrosine, &c., brought about by the pancreatic ferment-trypsin. It will be seen, on glancing through these enumerations of the unorganised ferments, that the greater number of those occurring in animals are found in the alimentary canal, and are concerned in the digestion of food. They all act best at a little over the temperature of the body (40° C.), their activity is hindered by a lower temperature, and they are destroyed by a high temperature. In a dry state pepsin and trypsin may be heated to 170° without harm,' but in a moist state a temperature below 100° C.2 is sufficient to destroy them. All fermentative processes require the presence of a certain amount of water. Free acid is harmful, except in a few cases, e.g. gastric digestion. The caustic alkalis also when present in more than very minute proportions hinder fermentation; as also do salts of the heavy metals, and ether, and chloroform in some cases. Quite small percentages of neutral salts (such as 0·004 per cent. of the sulphate of sodium, potassium, ammonium, or magnesium, 0.02 of various urates, 0.01 of sodium chloride or phosphate) have a very considerable inhibitory effect when pure solutions of pepsin or trypsin are used (Nasse,3 Heidenhain, A. Schmidt, E. Stadelmann 6). 4 Bert and Regnard state that organised ferments are killed by probable on further investigation that the formula of myronic acid may be modified, and that the ferment change will be found to be also one of hydrolysis (Will and Körner, Liebig's Annalen, cxxv. 263). By hydrolysis, one means the fixation of the elements of water, followed by decomposition into simpler products. The term should be distinguished from hydration, in which there is no such subsequent decomposition. 1 Huppe, Chem. Centralblatt, 1881, p. 745. The critical temperature at which the soluble ferments are destroyed varies with the different enzymes; the range of temperature is approximately 50°-75° C. 6 Zeit. Biol. xxv. 208. 3 Pflüger's Arch. xi. 4 Ibid. x. 5 Ibid. xiii. |