343 LECTURE XXI. 



into the active and movable condition ; these are the Ferments '. They appear to 

 originate from proteinaceous substances, always however in extremely small quan- 

 tities only, so that their existence in most cases can only be inferred from their 

 conspicuous action ; this action consists in their being able to convert very large, 

 perhaps indeed unlimited quantities of reserve-materials into the active state. The 

 ferments affect the latter in a certain sense as stimuli do irritable organs. In what 

 way this action takes place however is still questionable, though it differs from ordinary 

 chemical actions in that the ferment itself is not essentially altered during the process, 

 and does not even enter into a chemical combination. It must be added here, 

 however, that similar alterations are produced on carbo-hydrates, proteid matters, 

 and some other peculiar organic compounds (especially the so-called glucosides) 

 by acids, alkalies, and even by water at higher temperatures. Hence it is not 

 always certain in the present state of our knowledge whether, in a given case not 

 more exactly investigated, the changes of the reserve-materials and glucosides in 

 question are produced by actual ferments, or by certain vegetable acids or alkalies. 

 In this province of vegetable physiology, which has only been opened up during the 

 last few years, there is still much that is problematical and uncertain, so that we 

 are necessitated to depend to a large extent on the experience of animal physiology. 

 Nevertheless the facts already known concerning vegetable ferments quite suffice 

 to show that in this connection also, as in so many others, important agreements 

 exist between the vital processes of animals and plants, especially where fundamental 

 phenomena are concerned. 



With regard to the results of their action, two main categories of ferments may 

 be distinguished. In the one case the ferment effects only an insignificant chemical 

 change, as when starch, cane-sugar, or inulin are converted into glucose, or proteids 

 into peptones. In other cases, on the contrary, the ferment action consists in a very 

 profound chemical alteration, of such a nature that from one complicated organic 

 compound two or three simpler compounds very different in kind are produced. 

 The first category may be distinguished as merely alterative ferments, the second as 

 splitting ferments. To the latter belongs, for example, the Emulsin of the Almond, 

 by means of which its amygdalin becomes decomposed into glucose, prussic acid, 

 and oil of bitter almonds, and which is also able to break up numerous other 

 glucosides into glucose and other products. The case is similar with Myrosin, which 

 splits potassium myronate into glucose, oil of mustard, and potassium sulphate. Never- 

 theless these ferments, as well as the matters upon which they act, are of subordinate 

 importance, since both occur only in individual families or species of plants, and 

 because their significance for metabolism, for the purposes of growth itself, is in these 

 cases very questionable. 



The fact is quite otherwise with the first category of ferments, which I have 

 distinguished as merely alterative. These re-invigorate the plastic reserve-materials 

 distributed throughout the vegetable world; and although we have as yet by no 



' More details respecting the ferments are to be found in Schiitzenberger's book, 'Die 

 Gdhrungserscheinungen,' (Leipzig, 1876) ; and also in Pfeffer's Pflanzen-physiologie, %% 47, ,i)6. 59' 

 Both, however, are wanting in criticism of the phenomena. In this connection the best is un- 

 doubtedly Naegeli's ' Theorie der Gdhrung'' (Miinchen, 1879). 



