April 3, 1902] 



NA TURE 



525 



oxygen, it has now passed for practical reasons to the combustion 

 of sulphur dioxide to trioxide. In this case we are concerned, 

 no doubt, with slow reactions, although it may be admitted that, 

 for example, in the case of electrolytic gas, no formation of water 

 is perceptible at the ordinary temperature in the absence of a 

 catalyst. But the regularity of the alteration of the velocity 

 with the temperature justifies us in the opinion that after all 

 there i> a very small velocity of reaction even at the ordinary 

 temperature. The extremely small value is in accordance with 

 the general fact that a gas reaction takes place very slowly. 

 This important fact appears, for example, in the experiments of 

 Berthelot and Pean de St. Gilles. The ester formation from 

 acid and alcohol was compared in two experiments of the same 

 kind, in one case the substances being liquid, in the other 

 gaseous. Even if the experiment does not permit of an exact 

 calculation as to whether the retardation may be fully explained 

 by the great reduction of concentration, or whether, as is more 

 probable, it goes beyond that, it is not to the point. It is 

 sufficient to know that by transition to the slate of gas, the 

 velocity of the reaction is reduced to about l/ioooth. 



It is possible now to set up a theory of the accelerations 

 just mentioned. If we suppose that in the gaseous system, at a 

 given temperature, one part is replaced by a liquid or acquires a 

 density corresponding to the liquid state, then in this part the 

 reaction will take place proportionately more quickly, and the 

 liquid part of the materials will be converted into the final pro- 

 ducts If then the liquefying or condensing source is of such a 

 nature that it goes on condensing fresh quantities of materials 

 as fast as the old are being used, these will react quickly 

 and the result is acceleration of the reaction. That such is 

 the case in the action of platinum on gases is quite possible. 

 I do not wish to assert by this representation that the catalytic 

 action takes place in such a way, but only to point out a possi- 

 bility as to how it might take place. We should then have the 

 simplest and purest case of an accelerating intermediate reaction 

 to which I have already referred. 



As Prof. Bredig has recently told me, it is possible to 

 represent the mechanism of such an acceleration by means of a 

 fluid medium in which small masses of another fluid are sus- 

 pended. If this suspended liquid has the property that in it the 

 reaction of the substances present can take place more quickly 

 than in the main mass of the liquid, the portions of the reagents 

 residing there will be the first to undergo change. The products 

 will diffuse into the enveloping liquid, and thus new quantities 

 of reagents will enter, since diffusion is always at work regulating 

 the concentration. In this way the whole quantity of the 

 reagents will successively find a way through the suspended 

 liquid and react there, and the result is an acceleration of the 

 reaction. 



Bredig supposes that this [view may be applied to the case 

 where a catalyst is present in a colloidal state in the liquid. 

 As is known. Prof. Bredig and his pupils in a series of remark- 

 able investigations have demonstrated the manifold and 

 energetic catalytic actions which are brought about by colloidal 

 platinum and other colloidal metals prepared by him. He also 

 pointed out that the extremely active catalysts occurring in 

 nature, the enzymes, occur likewise in a state of colloidal solution 

 or suspension. 



These views have no other pretension than to be views which 

 can be brought to an experimental test. I must not omit to 

 draw attention to the fact that it is the view of catalysts as 

 accelerators that has made it at all possible to put forward 

 notions which can be so tested. Let anyone try to attain the 

 same end by means of molecular vibrations. 



{4) Enzymes. 



Berzelius had no doubt that the conversion of starch into 

 sugar by means of acids was to be classed with similar conver- 

 sions by means of malt extract. The same view was held by 

 Payen and Persoz, who isolated the active substance, diastase, 

 or at least prepared it in a concentrated form. The same view 

 holds good for Liebig and Wiihler, who in an excellent research 

 studied the decomposition of amygdalin under the catalytic 

 influence of emulsin. 



The later investigations of the laws of enzyme action have, in 

 my opinion, brought to light nothing which gives ground for a 

 fundamental distinction between the two kinds of action. On 

 the contrary, the researches of Bredig, before mentioned, have 

 displayed a much more thorough-going correspondence than 

 might have been expected. 



We shall look upon the enzymes, therefore, as catalysts 



NO. 1692, VOL. 65] 



which arise in the organs during the life of the cell and by whose 

 action it discharges the greatest part of its duties. Not only 

 are digestion and assimilation from beginning to end regu- 

 lated by enzymes, but the fundamental life activity of most 

 organisms, that is to say, the acquisition of the necessary chemical 

 energy by combustion in atmospheric oxygen, takes place with 

 the definite cooperation of enzymes, and without this would 

 be impossible, for free oxygen is known to be a very inert 

 substance at the temperature of organisms, and without an 

 acceleration of the reaction, the maintenance of life would be 

 impossible. 



Berzelius had already pointed to the decisive importance that 

 attaches to enzymes in the economy of the living being. As a 

 matter of fact, if we put the fundamental question, " what is 

 the physicochemical criterion of the phenomena of life?" the 

 answer will be, '* an automatically regulated production and use 

 of chemical energy, for the animation, maintenance and increase 

 of the living thing." We have three different means of influ- 

 encing the velocity of chemical reaction — temperature, concen- 

 tration and catalysis. Of these Aree, the first cannot be 

 obtained for the organism at its wilk We see, indeed, that in 

 the higher animals, in which especially complicated and delicate 

 functions are to be fulfilled, there is complete freedom from 

 the influence of temperature, inasmuch as they provide them- 

 selves with thermostatic appliances by means of which their 

 body temperature can be maintained constant between certain 

 limits. Concentrations are in many ways limited by the solu- 

 Wlity of the substances concerned. There remains only one 

 generally applicable means of regulating the velocity of the 

 reactions — the application of catalysts — and this without doubt 

 admits of the solution of the problem in ideal completeness. 



I must not go further into the physiological question, but I 

 did not wish to omit pointing out the importance of catalysis in 

 this direction. This seems to me to be at the present time 

 especially necessary. The older chemistry, with its facts and 

 theories, which were concerned with the preparation and the 

 systematic and genetic relations of substances, without regard 

 to the laws of equilibrium and change, has proved in many 

 respects unproductive in the explanation of physiological 

 phenomena, and it seemed as if chemistry and physics were 

 altogether unable to contribute anything decisive towards 

 solving the riddle of life. 



On the other hand, I should like to point out with all reserve 

 that physical and general chemistry, in the domain of which the 

 greater portion of this question lies, is a very young science. Those 

 of you who were present at the Naturforscher Versammlung in 

 1S92 will remember that it first, so to speak, " came out " there 

 like a full-grown young lady. Hitherto she has found so much 

 to do in her own house that she has only been able occasionally 

 to pursue her labours in other regions, but it cannot be denied' 

 that many a hand has wished to pluck the fruits without 

 knowing what to do with them. 



It is my full and repeatedly expressed opinion that by means 

 of the later advances of chemistry there lies before physiology a 

 development which will be in ni degree less important than that 

 which was brought about by Liebig in his time by the first 

 systematic application of chemical science. 



So far as the properties of the enzymes are concerned, these 

 have hitherto been investigated mainly in a qualitative way. 

 Quantitative work meets with the great difficulties which 

 lie in the alterability of the substance, associated, as a rule, with 

 the loss of catalytic power. The enzymes hitherto investigated 

 show essentially the chemical properties of albumenoids, but the 

 question of their chemical nature is by no means yet settled. \ 

 should like to express my conviction that a more thorough in- 

 vestigation will disclose other intermediate stages between 

 albumenoid products with which enzyme activilies have been 

 shown to be associated and the more simple compound sub- 

 stances of organic chemistry. Thus, for example, the catalytic 

 acceleration of some oxidation processes which are characteristic 

 of hemoglobin seems to be maintained in its non-albumenoid 

 derivatives, especially in hxmatin, and a following out of these 

 relations in the decomposition products of the colouring matter 

 of the blood would be of no slight interest. 



In a few cases in which the cause of the velocity of an enzyme 

 action has been studied in such a way as to be completely free 

 from objection, contradictory results have appeared ; while 

 some authors have found a thorough-going agreement with the 

 simple laws which are applicable to inorganic catalysts, others 

 have found discrepancies. 



