ZYMOLOGY FERMENTS AND FERMENTATIONS 227 



Invertase. Like maltase this enzyme is widely distributed in the vege- 

 table and animal kingdoms. It acts upon cane sugar, splitting it into 

 about equal parts of glucose and fructose. The ferment is analogous to 

 maltase. 



Trehalase. This ferment converts trehalose, a disaccharid found in 

 the group fungi and also in a variety of manna (insect manna, treha^a 

 or tigala), into two molecules. The ferment is found in species of Asper- 

 gillus and in other fungi. 



Melicitase. This ferment is found in several varieties of lower or 

 bottom yeasts, but is said to be wholly absent in all top yeasts. It splits 

 melibiose into d-galactose and d-glucose, in which action it is analogous to 

 lactase. 



Lactase. Lactase acts on milk sugar (lactose) only, changing this 

 disaccharid into d-glucose 'and d-galactose. The ferment was first dis- 

 covered in Saccharomyces kefir and in S. tyrocola. The pancreas contains 

 no lactase but it occurs in the small intestine of young animals, less in the 

 intestine of fully grown animals and is generally wanting in old animals. 

 Lactase is also said to occur in some species of bacilli. The comparative 

 scarcity of lactase-forming organisms explains why lactose is compara- 

 tively less liable to fermentation, than is cane sugar, for example. 



c. Polysaccharide (Diastase) Ferments. These ferments split up in- 

 soluble saccharine compounds into soluble sugars and are very closely 

 related to the diastases already mentioned. The principle enzymes of 

 this group are cytase which decomposes cellulose which is the chief con- 

 stituent of plant cell-walls. Inulase decomposes the inulin abundant in 

 many Compositae as in Taraxacum, Inula and in other genera. Pectinase 

 decomposes pectin and thus destroys the products of pectase which gives 

 rise to pectin. Seminase decomposes mannogalactan into mannose and 

 galactose and is very widely distributed in the seeds of higher plants, es- 

 pecially in seeds of the locust, of alfalfa and of fcenugreek. Carubinase 

 is similar to seminase and occurs in the germinating seeds of Ceratonia 

 siliqua (St. John's Bread). It converts the polysaccharide carubin into 

 carubinose, which is said to be similar and perhaps identical with d- 

 mannose. 



4. Glucoside Splitting Ferments. Glucosides are very important 

 active constituents of many of our most important medicinal plants. 

 These substances are not acted upon by the yeast ferments as maltase, in- 

 vertase and trehalase, with the one exception of the glucoside amygdalin 

 of bitter almonds. 



a. Emulsin. This is the most important of the glucoside splitting 

 ferments. It is widely distributed in the vegetable kingdom occurring 

 in higher plants as well as in the cryptogams. Among the phanerogans 



