154 METABOLISM 



Thus, in the hydrolytic decomposition of an ester by hydrochloric acid, alcohol 

 and acid are formed, but the alcohol unites again with the acid, water being 

 given off, and an equilibrium is brought about if the formation of the ester goes 

 on as rapidly as its decomposition. If enzymes behave in the same way as the 

 hydrochloric acid in this example, then they must be able to induce not only 

 a hydrolysis, but, under certain conditions, a synthesis also. Something 

 like this has been observed by HILL (1898). He obtained an enzyme 

 from yeast, which changes maltose into dextrose, allowed it to act on a 40 per 

 cent, solution of dextrose, and found that after a long time 14-5 per cent, of 

 the dextrose was changed into maltose. A synthesis took place when water 

 was withdrawn, and an equilibrium was reached when 14-5 per cent, of the 

 sugar was composed of maltose and 85-5 per cent, of dextrose. The con- 

 dition of equilibrium depended essentially on the concentration of the solution, 

 as the following summary shows : 



Amount of dextrose 

 originally present. 



40% 



20,, 

 10,, 



4 ,, 



a 



Amount of dextrose after the 

 action of the enzyme. 



85-5% 

 90-5 

 94-5 ., 

 98-0,, 



99-o 



Amount of maltose after the 

 action of the enzyme. 



14-5% 

 9-5 

 5-5 ,, 



2-0 



I-O ,, 



The more dilute the solution of dextrose the less the amount of maltose 

 formed. HILL'S work has been confirmed in many respects by WENT (1901), 

 and a reversible action has been established in the case of other enzymes as well 

 (lipase, HANRIOT ; maltase, EMMERLING, 1901). In spite of this reversible action, 

 it is quite obvious that we, as a rule, see only one aspect of the enzymic activity, 

 i. e. hydrolysis, and that when the products of the reaction have been 

 effectively removed, a complete hydrolysis of the products of the process will 

 be found to have taken place. 



The view advanced by HILL is opposed to that taken by TAMMANN (1892). 

 According to this investigator no reversible action occurs during enzymic activity. 

 He holds that when hydrolysis remains incomplete, the reason is that the enzyme 

 becomes altered into an inactive variety under the influence of the accumu- 

 lation of decomposition products. Further research is needed to determine 

 which view, HILL'S or TAMMANN'S, is the right one ; but if, as we have no doubt, 

 HILL'S theory be correct, then BREDIG would have to show that a formation 

 of hydrogen-peroxide took place in presence of his ' inorganic ferments ', if he 

 desired to establish a comparison between these bodies and organic ferments. 



The similarity between these substances does not seem to us to be very 

 great, and to be confined to the fact that enzymes and platinum solutions are 

 catalytic agents. Catalytic substances, however, belong to very diverse cate- 

 gories (OSTWALD, 1902). We might, indeed, doubt whether enzymes are cata- 

 lytic agents at all, seeing that many of the decompositions in question are not 

 perceptible in the absence of the enzyme. Starch, for example, under ordinary 

 conditions, produces no maltose in water ; and it would appear doubtful 

 whether we are entitled to regard the action of the enzyme merely as a case of 

 acceleration of a previously existent process. If we find, however, that 

 hydrolysis certainly occurs at higher temperatures without an enzyme being 

 present, and that the reaction gradually ceases when the temperature is 

 lowered, we cannot deny spontaneous hydrolysis at ordinary temperatures, 

 even if the products arising from the action do not make themselves apparent 

 perhaps till years afterwards. At all events the classification of enzymes in 

 the category of catalytic agents is the best hypothesis we can put forward 

 at present. 



After these general remarks on enzymes and on diastase in particular, let 

 us return to the consideration of the germination of seeds. Dissolution of 

 starch may be studied best in the seeds of Gramineae, which possess an especially 



