500 POPULAR SCIENCE MONTHLY. 



Together with sucrase and maltase may be grouped other euzyiaes 

 that split up the higher sugars into those of lower molecular weight, 

 such as lactase which converts lactose or milk-sugar into dextrose 

 and galactose, trelialase which splits up trehalose, a sugar obtained 

 from Syrian manna, into two molecules of dextrose, and raffinase and 

 melizitase which act upon certain of the higher polysaccharides. 



Coagulating enzymes. The gTOup of clotting or coagulating 

 enzymes includes two comparatively well-known enzymes, rennet and 

 plasmase or fibrin ferment. The use of rennet in setting curd for 

 cheese and in preparing the delicate dessert known as junket is gen- 

 erally familiar. The source of most of the commercial rennet is the 

 extract of the mucous membrane of the stomach of the calf ; this enzyme 

 is found also in many other young mammals during the period of lac- 

 tation. Eennet has been obtained likewise from several vegetable 

 sources; parts of the plant Galium are used in the country districts of 

 England to aid in the formation of curd in cheese-making, and the 

 peasants of the Italian Alps use the leaves of the butterwort {Pin- 

 guicula) for a similar purpose. The curdling or precipitation of the 

 casein by rennet is singularly dependent upon the presence of salts of 

 lime. A very minute quantity of rennet in the presence of calcium 

 salts will curdle a prodigious quantity of casein. It is in fact uncer- 

 tain whether rennet can act at all in the entire absence of calcium. In 

 the presence of calcium the potency of rennet ranks higher than that of 

 any other enzyme yet studied, one part of rennet being able to 

 coagulate more than 250,000 times its own weight of casein. 



The phenomenon of the clotting of blood is dependent upon a 

 variety of factors as yet imperfectly understood. That the fibrin or 

 solid portion of the clot is separated out from the blood plasma by the 

 action of an enzyme is, however, solidly established. The character and 

 mode of action of this enzyme — termed plasmase, or fibrin ferment — 

 are still quite obscure, although the fact that in mammalian blood the 

 enzyme originates from the leucocytes, or white blood corpuscles, seems 

 to be generally admitted. In birds the enzyme exists in the cells of 

 the tissues and not in the blood corpuscles. The blood of all verte- 

 brates with nucleated red corpuscles presents a marked resistance to 

 spontaneous coagulation; clotting, on the contrary, is almost imme- 

 diate among the mammals, which possess enucleated red corpuscles. 

 As is the case with rennet, calcium salts favor coagulation; their 

 presence seems, however, not to be necessary. 



Other clotting phenomena have been shown to be due to enzyme 

 action. The formation of jelly from the juices of various fruits and 

 berries is due to the gelatinizing or coagulating effect of an enzyme, 

 pectase, which acts upon pectose, a carbohydrate allied to cellulose and 

 occurring in many fruits and vegetables. 



