352 



NATURE 



[June 22, 1916 



incapable of further development. In anticipation of 

 this exhaustion, in 1880, a scheme had been prepared 

 for tapping the Watts River, the average daily flow 

 of which was estimated at 42 million gallons. The 

 execution of the project was, however, delayed, and it 

 was not until 189 1 that water from this source was 

 actually turned on, when the name of the system, 

 as well as of the river itself, was changed into 

 Maroondah. The aqueduct is 41 miles long, with 

 255 miles of open channel and twelve tunnels (three 

 over a mile in length). The total cost of the Maroon- 

 dah system amounted to 778,9442. 



By 1907 the population had increased to 536,540, and 

 still further sources of supply were found necessary. 

 In 1910, powers were granted to incorporate the 

 O'Shannassy and Upper Yarra watersheds, and by 

 1914 a supply of 20 million gallons per day was being 

 obtained from the former river bv means of an aque- 

 duct 485 miles in length. The Upper Yarra supplies 

 remain to be exploited at some future date. The 

 amount spent so far on the O'Shannassy scheme has 

 been 426,890/. 



THE MECHANISM OF CHEMICAL CHANGE 

 IN LIVING ORGANISMSA 



T F we take a general view over the large field of 

 ^ chemical reactions known, we notice that there 

 is a great variety in the rate at which these reactions 

 take place. Some, and especially those in which elec- 

 trical forces play a part, reactions between inorganic 

 ions, are practically instantaneous. They are familiar 

 to all in the precipitations of the anal3''tical chemist. 

 Others, such as the hydrolysis of cane-sugar by water, 

 are so slow as to be incapable of detection at ordinary 

 temperatures, unless a very long time is allowed. 

 There are, moreover, all possible stages intermediate 

 between these extremes. Reactions between carbon 

 compounds are, generally speaking, comparatively 

 slow; but, as the name "organic" indicates, they are 

 the characteristic chemical changes of the living cell. 



Early workers in the domain of physiological chem- 

 istry — Schonbein, for example — were struck by the fact 

 that reactions which require, in the laboratoi'y, power- 

 ful reagents, such as strong acids and high tempera- 

 tures, to make them take place at a reasonable rate, 

 occur rapidly in the living organism at moderate tem- 

 peratures and in the presence of extremely weak acids 

 or alkalis. I may refer to the decomposition of pro- 

 teins into their constituent amino-acids, which is a 

 part of the normal process of digestion, but, when 

 ordinary laboratory methods are used, requires boil- 

 ing for several hours with concentrated hydrochloric 

 or sulphuric acid. 



The problem before us, then, is to discover how a 

 slow reaction can be made to go faster. The most 

 obvious and well-known method of doing this is by 

 raising the temperature; but this is clearly out of the 

 question in living cells. Another possibility is to make 

 use of mass action, increasing by some means the 

 effective concentration of the reacting substances; in 

 this way the number of contacts per unit time would 

 be raised. This is possible in the cell. There remains 

 a third, the formation of an intermediate compound 

 with another substance. This compound may be 

 supposed to be both formed and again decomposed 

 at a rapid rate, so that the total time taken is much 

 less than that of the original reaction. 



Now it is evident that something of the kind con- 

 templated by these two latter possibilities is at the 

 bottom of the process called "catalysis" by Berzelius. 

 Tills chemist directed attention to the numerous cases 



• 1 Abridged from a discourse delivered at the Royal Institution on March 

 24, by Prof. W. M. Payliss, F.R.S. 



NO. 2434, VOL. 97] 



known, even at his time, where the presence of a 

 third substance brings about an enormous accelera- 

 tion of a reaction, without itself taking part in it, 

 so far as appears at first sight; at all events, this 

 third substance reappears at the end unchanged. An 

 example is the effect of finely divided platinum on 

 hydrogen peroxide. Similar phenomena were known 

 to Faraday, and described by him about the same 

 time, but without giving them a special name. 



Agents of this kind were soon discovered to be pre- 

 sent in living cells. Such catalysts are called, for 

 convenience, "enzymes," as suggested by Kiihne, 

 although there is no real scientific necessity for the 

 name. That of " ferments " is still sometimes used, 

 and is not now liable, as it was in Kiihne's time, to 

 cause confusion by application to living microbes. 



Since catalysts are, as a rule, found unchanged at 

 the end of their work, it is clear that they do not 

 themselves afford energy for the purpose. Indeed, the 

 energy change of a catalysed homogeneous system is 

 the same as that of the reaction when proceeding at 

 its ordinary slow rate. How, then, do they act? 



The first thing to note with respect to enzymes is 

 that they are capable of activity in media in which 

 they are insoluble. Whatever may be the nature of 

 this activity, therefore, it is exerted by the surface of 

 the catalyst. We may then reasonably ask, as the 

 most obvious hypothesis, is there ground for holding 

 that the increased rate of reactions brought about by 

 enzymes is effected by increase of concentration of the 

 reagents at the surface and consequent acceleration 

 of the reaction by mass action? We know that sub- 

 stances which lower surface energy of any form are 

 concentrated at such boundary surfaces. The process 

 is well known as "adsorption," and is a consequence 

 of the operation of the principle of Carnot and 

 Clausius, which states that decrease of free energy 

 always occurs, if it is possible for it to do so. In 

 fact, such an explanation was given by Faraday of the 

 effect of metallic platinum in causing combination of 

 oxygen and hydrogen gases. Although the name "ad- 

 sorption " was not used in this description, Faraday 

 had very clear ideas of the process, and gives several 

 interesting cases. He showed that the necessary con- 

 dition for the activity of platinum in the case referred 

 to is a chemically clean surface, in order that the 

 gases may condense on it. It matters not whether 

 the removal of deposit is effected by mechanical polish- 

 ing ; by the action of acid or of alkali ; by oxidation or 

 reduction — making it either anode or kathode in an 

 electrolytic cell will serve. It should be mentioned 

 that this view did not receive universal acceptance, but 

 the fact that it recommended itself to the keen insight 

 of Faraday is powerful evidence in its favour. 



I would not venture to state that this hypothesis is 

 yet in a position to explain all the facts met with in 

 the action of enzymes themselves, but it is remarkable 

 how many receive a satisfactory account. We are at 

 once confronted by the difficulty of the considerable 

 number of different enzymes. But we must not forget 

 that adsorption is controlled by a great number of 

 factors in addition to mechanical surface tension. All 

 those properties which suffer modification at phase 

 boundaries: play their part — electrical charge, solu- 

 bility, compressibility, even chemical reaction itself, 

 may be mentioned. Moreover, as Hardy has pointed 

 out, the act of condensation in itself may well be 

 accompanied by the manifestation of molecular forces 

 which result in increased chemical potential of the 

 reacting substances. It is clear that experimental 

 decision of the questions involved is almost impossible 

 until we have in our hands pure preparations of 

 enzj'mes. We cannot as yet exclude the possibility 

 of the formation of intermediate chemical compounds 



