Nov. 26,1917 
Enzyms of Milk and Butter 
439 
EXPERIMENTAL WORK 
I. INVESTIGATIONS CONCERNING GALACTASE 
The normal proteolytic enzym of milk, which aids in the slow decom¬ 
position of milk proteins into peptones, amino acids, and ammonia, was 
given the name “galactase” by Babcock and Russell (j-5). This name 
is unfortunately not in accord with the present system of nomenclature, 
and the enzym ought properly to be called “casease” or “lactalbumi- 
nase”; but, since the name suggested by Babcock and Russell has come 
into common use and its significance is properly understood, we decided 
to continue its use. 
Before undertaking the proposed studies of the galactase content of 
milk, cream, skim milk, buttermilk, and butter it was necessary to 
determine upon certain details of technic which had not been satisfac¬ 
torily worked out by former investigators. This preliminary work may 
be briefly summarized as follows: 
(a) Length of period of action. —Previous experimental data 
give quantitative measures of proteolytic activity for periods varying 
from 1 hour for certain pepsin studies (8) up to the practically prohibitive 
time of nearly 3 years for galactase ( 14 ). The time in which most investi¬ 
gators have allowed galactase to act, in order to obtain comparative 
results, has varied from 30 days to 1 year. This appears to be unneces¬ 
sarily long. The analytical data presented by Babcock and Russell give 
an average increase in the soluble-nitrogen content of a number of sam¬ 
ples of skim milk, when expressed as percentage of the total nitrogen, of 
13.49 per cent for the first 8 days and only 5.66 per cent for the following 
12 days. One sample of skim milk increased 26 per cent in soluble nitro¬ 
gen during the first 7 days, 2 per cent the following 7 days, and to increase 
the soluble nitrogen content another 26 per cent required a period of 3 
days. There is very little difference in the comparative galactase con¬ 
tent of various skim milks when analyses made at the end of 7 days or 
of 6 months are compared. In the present work the period of action 
was limited to 4 days, since it was found that the soluble nitrogen in 
skim milk increased 10 or 12 per cent during this time. 
(1 b ) Measurement of hydrolysis by means of the ninhydrin 
reaction. —The ninhydrin method, as proposed by Harding and 
MacLean (11) for the determination of amino-acid or nitrogen, was com¬ 
pared with the official method of the Association of Official Agricultural 
Chemists (26) for determining the increase in soluble nitrogen in differ¬ 
ent samples of milk due to protease action (Table I). In the ninhydrin 
determination the sample was diluted 1 to 10, and 1 c. c. of this used in 
each analysis, but the results were calculated to the 10 c. c. basis. Bac¬ 
terial action was inhibited by 0.5 per cent of chloroform. All samples in 
all the work reported in this paper were incubated at 40° C. for four days. 
