LACTASE. 531 



however, being only effected slowly and with difficulty. Accord- 

 ing to GST (Fl.) the reaction is not complete unless one part of 

 milk sugar be boiled with four parts of 2 per cent, sulphuric acid 

 for six hours, or with ten parts of the same acid for four hours. 

 URECH (T.) states that a solution of lactose containing 11.38 per 

 cent, of hydrochloric acid will remain unaltered in the cold, even 

 after the lapse of twenty-eight days ; and that it is only when the 

 proportion of acid reaches 32 per cent, that the sugar is almost 

 completely decomposed within twelve hours at 23 0. Milk-sugar 

 solution containing 4 per cent, of oxalic acid will remain unaltered 

 after boiling for eight days; and according to JONES (I.) citric 

 acid also is incapable of hydrolysing lactose. It therefore appears 

 impossible for the lactose in a liquid containing that sugar to be 

 decomposed merely by the organic acids formed by acid bacteria. 



Like all di- and poly-saccharides, milk sugar is capable of being 

 fermented directly, but requires to be previously split up into its 

 components by a special enzyme, lactase. 



As already mentioned on p. 163, vol. i., Beijerinck discovered 

 this enzyme to which the name, lacto-glucase, has been applied 

 by E. O. von LIPPMAN (IV.) in Sacch. Kefyr and Sacch. tyrncola, 

 According to E. FISCHER (XV.), lactase cannot be extracted direct 

 from lactose yeast with water, the cells having first to be triturated 

 with ground glass, in order to bring the enzyme into solution. 

 Lactose yeast that has been killed by means of chloroform also 

 exerts a powerful hyclrolytic action on lactose solutions. On the 

 other hand, the enzyme can be readily extracted from Kefyr 

 granules by water, on which account E. Fischer proposed to name 

 it kefyr lactase in contradistinction to yeast lactase. This kefyr 

 lactase has greater powers of resistance than maltase to the action 

 of concentrated alcohol. 



BUCHNER and MEISENHEIMER (I.) recovered from Armenian 

 mazun yeast an expressed juice containing lactase. This yeast 

 lactase will not diffuse through parchment paper, and is therefore 

 like the enzyme from Monilia Candida (see p. 446, vol. i.) an 

 endoenzyme. 



Among the fungi, Mucor javanicus according to WEIIMER 

 (XIII.) ; M. Ca'ntbodja according to CHRZASZCZ (I.); and 

 Allescheria (Enrotiopsis) Gayoni according to LABORDE(VIII.) 

 appear to contain this enzyme. DUCLAUX (XXX.) found that the 

 matured mycelium of Aspergillus niger and Penicillium glaucum 

 secretes lactase; but the point needs further investigation (see 

 p. 363, vol. ii.). 



According to E. FISCHER (XV.), emulsin which in any event 

 is a mixture of enzymes will also decompose lactose ; and 

 BEIJERINCK (XX.) and BERNHEIM (II.) report the capacity of a 

 barley enzyme for hydrolysing milk sugar. 



Lactase is widely encountered in the animal kingdom, and has 

 been found by ROBERT (IV.) in the juices of numerous lower 



