616 
Milk is frequently pasteurized by simply placing the bottle of milk 
as it is received, in a pot of water, the water boiled for a variable 
length of time, and then cooled. As will be shown by the following 
experiments, this is not always an entirely safe procedure for the 
purposes of home pasteurization. The depth of water in yhich. the 
bottle is immersed markedly affects the results. The neck of the bot- 
tle must always project above the water, and unless the pot has a lid 
the upper layers of the milk may escape heating, especially if the 
contents have not been well shaken up and the thick cream, which is 
in part turned to butter as a result of agitation on the delivery wagon, 
prevents circulation of the fluid. 
It will be seen in some of the experiments made by myself in the 
Hygienic Laboratory that contrary to what ipight be expected from 
the physics of fluids, the top layers of the milk are sometimes not as 
hot as the bottom or require a much longer time to heat up. 
Experiment No. 1. 
Pint mixed market milk. 
Bottle immersed in water to its lip. 
Distinct cream line from standing over six hours before heating ; thick cream, 
almost butter, floating on top. 
Water 
temper- 
ature. 
Milk temperature. 
Top. Bottom. 
Time. 
Colonies 
per loop 1 
in agar. 
Remarks. 
° C. 
° C. 
° C. 
Minutes. 
26 1 
26.5 
25. 5 
(a) 
30 
26.5 
26.5 
2 
(a) 
40 
27 
28. 75 
4i 
(a) 
50 
30 
32 
7 
(o) 
60 
35 
39 
9! 
(a) 
70 
41 
45 
12 
(«)' 
75 
45 
49 
13 
(°) j 
80 
50 
53. 5 
14! 
(a) 
83 
1 Simmering. 
85 
55 
58 
15! 
(a) 
87 
58 
60. 5 
16! 
(*) 
88 . 
60 
62.5 
16| 
( 6 ) 
91 
63 
66 
17 2 
( 6 ) 
92.5 
65 
68 
18! 
(*>) 
97 
70 
73 
19| 
(<D 
98 
71 
75 
20 
( c ) 
Boiling. 
100 
75 
80 
21! 
(<0 
100 
78 
83 
23 
(<0 
100 
80 
85 
23! 
(d) 
a Innumerable. b Somewhat less innumerable, c Distinctly less innumerable. d About 200,000. 
