XXXIV INTRODUCTION 



the various chemical reactions, but that it is transformed from the potential 

 into the kinetic condition, or vice versa. In the combustion of coal, for example, 

 heat is liberated, while by the reverse process, the decomposition of carbon 

 dioxide, heat is stored. Since combustibility is a characteristic of all organic 

 compounds, their formation from carbonic acid must therefore be accompanied 

 by an intake of heat and a storing of potential energy, which may be subse- 

 quently liberated during conbustion. In all investigations concerning the 

 transformations of materials in plants it must be clearly stated whether energy 

 is stored or released, since only thus can it be clear what is the meaning and im- 

 portance of such transformations in the general activity of the organism. 



At first glance, some phenomena seem to present exceptions to the principle 

 of the conservation of energy and to exhibit no quantitative relation between 

 cause and effect. For example, a small spark may cause the explosion of an 

 enormous amount of gunpowder and thus produce tremendous destruction. It 

 might seem here that a small cause has entailed a great effect; in reality, however, 

 the same amount of energy was liberated in the explosion as was originally 

 present — in a potential form — in the gunpowder. The spark served only to 

 initiate the change of this energy from one condition to the other. A small 

 concussion of the air is often sufficient to cause the fall of a huge boulder from 

 a great height, but the work thereby performed is exactly equal to the amount 

 necessary to replace the boulder in its original position. The pressure of the 

 air serves here as the trigger that produces the discharge. 



In considering the great importance of enzymes in the chemical processes of 

 plants it must be realized that their part in the various reactions does not con- 

 sist in a simple release. Bredig was quite right when he said, "We still find 

 much vagueness in the text-books as to whether, in this matter of the contact 

 action of substances such as acids and enzymes in the hydrolysis of esters, 

 carbohydrates, glucosides, etc., we have to do with the initiation of a reaction 

 incapable of occurring by itself, or only with the acceleration of a reaction that 

 takes place so slowly (in the absence of the catalyzer) as to be almost imper- 

 ceptible, but that is nevertheless already in operation. The question is, there- 

 fore, to use a mechanical figure, whether the enzyme sets into operation a 

 machine previously held at rest by a trigger-pin, or whether the enzyme serves 

 only as a lubricant to hasten the action of the machine (the chemical reaction), 

 which would otherwise be very slow and almost imperceptible, because of great 

 resistance." 1 Enzymes accelerate reactions that would otherwise progress but 

 slowly (Wilh. Ostwald) and they are thus comparable only to the "lubricant.'"* 

 On the other hand, the touch that causes a reaction-movement of the leaves 

 of Mimosa pudica (the sensitive plant) may be regarded as a typical example of 

 a discharge or release. 



The causes that produce certain phenomena and the conditions that first 

 render them possible must also be differentiated. For instance, if solid calcium 



i Bredig, G., Die Elemente der chemischen Kinetik, mit besonderer Beriicksichtigung der Katalyse 

 und der Fermentwirkung, Ergeb. Physiol. 1 : 134-212. 1902. 



d Enzymes frequently appear to alter the end-point of a reaction, so that it proceeds 

 farther in their presence than without them. — Ed. 



