518 



Dr. E. F. Armstrong. 



[Apr. 5, 



the enzyme with both the sugar and water; this theme was further 

 developed in his Presidential Address to the Chemical Society in 1895.* 



Hydrolysis of Milk Sugar by Lactase. 



Table 1. — Solutions were compared containing equal amounts of milk 

 sugar to one of which an equal weight of a mixture of equal parts of 

 glucose and galactose was added : it will be seen that this addition 

 reduced the rate to nearly half its value. In this and all subsequent 

 tables the figures indicate the percentage of biose hydrolysed : — 







+ 5 grammes 







glucose and 



Time in 



10 grammes milk 



5 grammes 



hours. 



sugar per 100 c.c. 



galactose. 



1 



1-3 % 



0-88 



2 



2*2 



1-34 



4 



3-37 



1-82 



6 



3-8 



2-22 



24 



5-55 



3-19 



48 



6-45 



3-64 



Table 2. — The effect of glucose, of galactose and of an equal weight 

 of a mixture of both on a 10-per-cent. solution of milk sugar are 

 contrasted in the following table : — 



+ 5 grammes 

 galactose and 



Time in + 10 grammes 5 grammes + 10 grammes 



hours. galactose. glucose. glucose. 



19 18-2 22-8 22-9 



24 21-0 25-0 25-6 



44 25-6 29-5 29-5 



67 30-9 34-8 34-8 



190 38-7 44-8 44-8 



Table 3. — That the retardation is produced almost entirely by the 

 galactose and that glucose or fructose are almost without influence is 

 shown by the following comparisons : — 



5 grammes 



Time in 



milk sugar 



+ 5 grammes 



+ 5 grammes 



+ 5 grammes 



hours. 



per 100 c.c. 



glucose. 



fructose. 



galactose. 



4 



18-0 



17-6 



18-0 



16-0 



22 



59-2 



59-6 



59-6 



47-4 



28 



65-6 



65-4 



65-4 



52-0 



69 



81-4 



78-4 



80-2 



61-6 



* ' Trans.,' vol. 67, p. 1136. 



