CHEMICAL COMPOSITION AND GENERAL REACTIONS. 103 



In conclusion, the reversible action of ferments, which has 

 recently been established, must be briefly considered. It has long 

 been known that the hydro ly tic decomposition effected by ferments 

 is never carried to an end, and it is usually stated that this is owing 

 to the fact that a gradual increase in the production of decom- 

 position-products inhibits the action of the ferments in question. In 

 the light of more recent investigations, however, this explanation is 

 not satisfactory. It has been demonstrated that maltase, when 

 added to a solution of maltose, will cause inversion of the latter to 

 glucose. An end-reaction is then not obtained ; but if this solution 

 is now added to a solution of glucose in turn, at a time when further 

 inversion does not occur, it will be noted that a retransformation of 

 glucose to maltose takes place, which, however, is likewise not 

 complete. It thus appears that the ferment is not only capable of 

 causing the hydrolytic decomposition, but also the synthesis of mal- 

 tose ; but that in so doing, its action ceases as soon as a certain 

 equilibrium of reaction has been established. This reversible action 

 on the part of ferments is, of course, of the greatest interest to the 

 physiological chemist, in showing that the complex syntheses which 

 take place in plant-life may, to a certain extent at least, be referable 

 to such action, and to forces which are probably also at work in the 

 non-organized world. 



Further research will show whether this action is common to all 

 ferments. 



Chemical Composition and General Reactions. Of the chem- 

 ical composition of the ferments but little is known that is definite. 

 This is owing to the fact that isolation of any one of the ferments in 

 a chemically pure form has thus far not been accomplished. They 

 apparently contain nitrogen, and are usually regarded as albumi- 

 nous substances ; but it is still a matter of doubt whether this is 

 actually the case, and it is possible that the supposition of their 

 albuminous nature is owing to their being contaminated with 

 albumins. 



Like the albumins, they are as a class non-diffusible. They are 

 soluble in water, and can be precipitated from their aqueous solu- 

 tions by salting with ammonium sulphate or by the addition of 

 strong alcohol. 



When kept under alcohol for any length of time some of the fer- 

 ments, such as pepsin and diastase, are rendered inactive and are 

 apparently coagulated, while the activity of others, such as the 

 fibrin ferment, remains unaffected. 



Characteristic general reactions, which are common to all fer- 

 ments, are unknown. Formerly it was supposed that they all pos- 

 sessed the power of decomposing hydrogen peroxide, but it appears 

 that this property does not belong to the ferments proper, but to 

 adherent particles of protoplasm. As a matter of fact, it is possible 

 in a number of ferments to destroy this power of decomposing 

 hydrogen peroxide without influencing their specific activity in the 



