§ VII.] Relation to the substratum. Enzymes. 69 



medium dissolved substances, which in the very minute quantity 

 in which they are excreted are able to give rise to other changes 

 in the substratum than those which belong directly to the 

 process of fermentation. Analogous products with analogous 

 effects are often obtained from other sources also, for instance 

 in Fungi which do not excite fermentation, and on certain 

 organs or in the cells of higher organisms, even of plants 

 containing chlorophyll. The Fungus of beer-yeast, for example, 

 Saccharomyces Cerevisiae, excretes a substance which inverts 

 cane-sugar in solution, as the phrase is, that is by absorbing 

 water splits it into glucose and laevulose (grape-sugar and fruit- 

 sugar). By means of a similar excretion Bacillus Amylobacter 

 breaks up cellulose into products soluble in water. The 

 cells of germinating seeds produce a body, diastase, which 

 breaks up starch-granules into dextrin and maltose. Substances 

 of this kind are known as enzymes or unformed or unorganised 

 ferments, in German terminology simply ferments. The ter- 

 minology of the French schools consistentlycarriedout,especially 

 by Duclaux, terms them generally diastases, and then for the 

 separate cases invents special words, all having the same ending, 

 as amylase, saccharase (' sucrase' !), casease, and so on, reserving 

 the word ferment, as we have learned, for the living ferment- 

 organisms themselves. Enzymes, as has been already intimated, 

 are either unorganised bodies or bodies with a definite form, 

 soluble in water, and are all allied as regards chemical character 

 to the proteid compounds. They can with proper manage- 

 ment be separated from the organisms which produce them 

 without putting an end to their activity. Their characteristic 

 mark as a rule is the power which they possess of causing 

 chemical changes, chemical separations, without passing them- 

 selves into the final products of these changes and so losing 

 their active powers. Their effects are specifically different in 

 every case, and they are accordingly distinguished, as in the 

 examples cited, into inverting, sugar-forming, and other enzymes, 

 to which may be added those that, Uke the pepsin of the gastric 



