METABOLISM AND GROWTH 217 



tackled the problem of the mode of action of these 

 mysterious bodies that appeared to be capable of inducing 

 profound changes in other substances without themselves 

 undergoing any alteration in the process. Although 

 most work was carried out on the first enzyme to be 

 recognised — diastase — it was not long before other 

 similar bodies were discovered and investigated. Thus 

 in 1887 Le Clerc du Sablon extracted from the artichoke 

 an enzyme which dissolved inulin and which he termed 

 "inulase"; in 1888 Marshall Ward isolated from a 

 lily-disease fungus a substance able to dissolve cell walls, 

 to which the name " cytase " was given, and its occurrence 

 in seeds with sclerotic endosperm, such as is found in 

 many Palms, was proved ten years later by Brown and 

 Morris, Gardiner, Bourquelot and Herissey, and others. 

 Similarly the transformation of cane-sugar was found 

 to be due to an enzyme called " invertase," and several 

 other sugar-altering ferments were rapidly added to the 

 list, such as maltase, glucase, lactase, etc. The glucosides 

 also appeared to require the services of such enzymes 

 as emulsin, myrosin, etc., while the proteins had their 

 specific enzymes, such as trypsin and erepsin, and fats 

 were acted on by lipases of various types. In short, it 

 soon became apparent that enzymes played a most 

 important part in all metaboHc changes, and that for 

 each reserve the protoplasm was able to call into existence 

 an appropriate enzyme, when it became necessary to 

 transform the reserve from a resting condition into a 

 body capable of passing through cell walls. 



Assimilation of Plasta 



If enzyme action be a subject of investigation bristling 

 with difficulties, assimilation, or the actual appropriation 

 of plasta by the protoplasm, is a problem that, as yet, 

 we have been quite unable to unravel. The subject is, 

 all the same, a fascinating one, for until tlic riddle is 



