333 
destroyed by boiling or by heating the milk above certain tempera- 
tures. On account of the important bearing which the thermal death 
point of milk ferments may have on the pasteurization of milk the 
following data relative to this subject are here submitted: 
Galactase . — According to Babcock and Bussell (19), the destruc- 
tion temperature of galactase, the proteolytic enzyme of milk, is 
somewhat higher than the thermal death point of trypsin. So far 
as its proteolytic activity is concerned, these observers found it 
to be weakened by heating for ten minutes at T6°-80° C. That 
such is the case may be seen from the following table, in which is 
shown the percentage of soluble nitrogen present at the end of fifty- 
three days in milks which had been heated for ten minutes at the 
temperature indicated. 
TABLE I. 
Temperature to 
which the ga- 
lactase was 
heated for 10 
minutes before 
being allowed 
to act on the 
milk. 
i ! 
Per cent of 
soluble nitro- 
gen after 
53 days at 
37° C.a 
78—80° C. 
0.05 
76 
.05 
71 
.12 
65 
.20 
60 
.20 
“ The soluble nitrogen originally present in the milk used in these experiments was found 
to be 0.05 per cent. 
Similar tests were made upon the proteolytic activity of galactase 
towards gelatin, using Fermi’s (20) method. Equal amounts of the 
galactase solution were poured over the surface of carbolized gelatin 
contained in test tubes and kept under observation seven weeks. 
The results of this series of experiments is given in Table II. 
TABLE II. 
L+ + =rapid digestion; + =digestion by galactase; — =no digestion.] 
Reaction of the galactase solu- 
tion. 
Temperature (°C.). 
Alkaline. 
Neutral. 
Acid. 
N/10. j 
N/20. 
N/10. 
65 
- 
- 
+ -i- 
- 
70 
_ 
_ 
_ 
— 
75 
80 
Control 
+ 
-h-i- 
- 
