118 THE FERMENTS. 



8. Ferments which Cause the Cleavage of Glucosides.^Such fer- 

 ments are quite common among invertebrates, and are especially 

 abundant in the higher plants. Examples are the emulsin or synap- 

 tase of bitter almonds, the myrosin of mustard seeds, and other 

 Cruciferce, etc. 



9. The nucleases, viz., ferments which are capable of causing the 

 cleavage of the nucleinic acids. This group also includes the fer- 

 ments which are concerned in the transformation of guanin and 

 adenin to xanthin or hypoxanthin respectively, viz., guanase and 

 adenase. 



All these ferments are characterized by their hydrolytic action 

 and must be differentiated from the oxidation ferments (see below). 

 Occupying an intermediate position between the two groups are : 



10. Ferments which are capable of splitting off carbon dioxide 

 from certain bodies. Ferments of this order are but little known, 

 but their presence is indicated in various ways. Emerson has 

 shown that a ferment belonging to this class occurs in the pancreas, 

 and is characterized by its ability to form oxyphenyl-ethylamin from 

 tyrosin by splitting off CO 2 . A similar ferment apparently occurs 

 in the liver and may be responsible for the transformation of 

 cy stin acid to taurin. 



11. The Oxidation Ferments. These are ferments which are inti- 

 mately concerned in the endocellular oxidations. They can be 

 divided into three groups. 



(a) THE OXYDASES (oxygenases). These take up molecular 

 oxygen with the formation of peroxides. They occur especially 

 widely distributed in the vegetable world. 



(6) THE PEROXYDASES. These contain manganese and alumin- 

 ium and in some instances iron and possibly copper. They are 

 quite stable and decompose hydrogen peroxide. In themselves 

 i. e., in the absence of peroxides they are incapable of causing oxi- 

 dations, but they increase the power of oxidation of the peroxides 

 very materially. 



(c) THE KATALASES. These decompose hydrogen peroxide kat- 

 alytically with the liberation of oxygen, but have not been shown to 

 be oxidizing agents themselves. 



Conjointly the oxygenases and peroxydases are also spoken of as 

 oxydases. Their mode of action consists essentially in the with- 

 drawal of two atoms of hydrogen with the formation of water, and 

 the occasional addition of one atom of oxygen. At times, however, 

 a more energetic oxidation is observed. The peroxydases are of 

 supreme biological interest owing to their power of decomposing 

 peroxides, which, according to Engler's views, form the starting- 

 point of all oxidations in the animal body. 



Aside from the common test for oxydases, viz., blueing of tincture 

 of guaiac, phenolphthalin may also be employed ; this is oxidized to 

 phenolphthalein, which may then be estimated eolorirnetrically. The 



