ENZYMES. 67 



first be reduced to glucose (grape-sugar), before they can be used as food by plants. 

 When no invertase has been detected the general hypothesis has been that this 

 inversion was due to the direct action of the protoplasm, but the recent isolation by 

 Buchner and others of an invertase (Zymase) from yeast, in which it was long believed 

 that none existed, once more emphasizes the uncertainty of negative conclusions. 

 Diastase is common. Is there more than one kind, i. e., a sort which can only 

 convert the starch into amylodextrin and another which converts it into maltose 

 and dextrine ? In many cases, when the organism is grown on potato, the con- 

 version is carried only a little way and stops, there being always a copious purple 

 or red-purple reaction with iodine. In other cases, e.g., when Bacterium campestre 

 is grown on potato, the starch conversion is so complete that after a few weeks there 

 is little or no color reaction when the potato-cylinder is mashed up and iodine water 



added. What makes this difference? 



A substance capable of dissolving the middle 

 lamella appears to be common to all bacterial plant 

 parasites and a true cytase presumably occurs, but 

 much additional study is necessary. Probably 

 several enzymes are confused under this name, 

 just as several chemically different substances are 

 still called "cellulose." The substance which 

 dissolves the middle lamella in some cases is prob- 

 ably ammonium oxalate. The writer has not been 

 able to dissolve it by means of pure oxalic acid, 

 but that of turnips softens in ammonium oxalate. 

 The lab or rennet ferment is rather common. 

 Its action should not be confused with the curdling 

 of milk due to the formation of acids. Tests may 

 be made in litmus milk. Is there more than one 

 kind of such ferment? Some organisms coagu- 

 late the milk promptly into a solid mass which 

 finally shrinks, extruding whey. Others cause the 

 Fig- 58,* casein to separate out of the fluid very slowly as a 



multitude of separate particles which only become compacted very slowly. 



The writer has not met with the oxidizing enzymes, unless the substance in 

 bacterial cultures which causes rapid evolution of oxygen from hydrogen peroxide is 

 such an enzyme, as Dr. Loew maintains (Bibliog., XLV). Many other enzymes 

 undoubtedly occur and play their part. The student should search for emulsin, 

 lipase, lactase, maltase (glucase), etc. 



All known enzymes when freely exposed to steam heat are destroyed at tempera- 

 tures considerably under 100 C. They are less sensitive to heat than the bacteria 

 themselves, but are destroyed by a few minutes exposure to temperatures 15 to 30 C. 

 (moist heat) above the thermal death-point of the organisms which have produced 



*Fic. 58. Thick-walled Kitasato flask for filtration or evaporation in vacua, etc. Much re- 

 duced. 



