474 
lus be discovered in the corresponding serum at the end of six hours. 
This agrees with the number of colonies upon the agar plates. 
The heated serums gave quite a different picture under the micro- 
scope. Many organisms were found, lying singly, in small and long 
chains, and in dense clusters. This corresponded to the innumerable 
growth upon the agar plates. 
RELATION TO PHAGOCYTOSIS. 
Milk contains many leucocytes and it therefore seems reasonable 
to assume that active phagocytosis takes place in the fresh raw prod- 
uct. A priori it seemed to us that this might account for the germi- 
cidal property of milk. This assumption was apparently confirmed 
when we found that stained smear preparations showed but few if 
any bacteria in the cells in the fresh milk just after inoculation with 
bacterial cultures, while similar preparations made from the same 
milk eight hours later, kept at 37° C., showed numerous bacteria in 
some of the cells. 
The following experiments, however, demonstrate that the ger- 
micidal power of milk is independent of its cellular contents. The 
leucocyte-free milk is quite as active as the leucocyte-rich sediment 
obtained by centrifugation. 
Table Xo 15. 
[Milk from a healthy cow (No. 2) was centrifuged for twenty minutes at 1,500 revolutions 
per minute. Part of the supernatant fluid was passed through a Berkefeld filter and a 
clear bluish serum obtained. Five sets of tubes were inoculated with 24-hour agar 
cultures, (1) the filtered clear serum, (2) the supernatant fluid free from leucocytes, 
(8) the sediment rich in leucocytes, (4) the original whole milk, and (5) sterilized milk. 
The inoculations were made three hours after milking.] 
Bacteria 
' per loop, 
I at once 
after inoc- 
I ulation. 
Bacteria per loop after 
8 hours at 37° C. 
Shaken ' 
moderately 
before ' ! 
planting. ' 
Vigorous 
agitation 
before 
planting. 
B. typhosus in filtered milk serum. 
22,000 
10,000 
B. typhosus in leucocyte-free supernatant fluid 
B. typhosus in leucocyte-rich sediment 
B. typhosus in whole raw milk 
B. typhosus in sterilized milk (control) 
19.000 
32.000 
3,500 
16.000 
1,900 
3,600 
1,200 
oJ>160,000 
15,000 
B. lactis aerogenes in filtered milk serum 
B. lactis aerogenes in leucocyte-free supernatant fluid 
33,000 a 6 330, 000 I 
4, 000 210 ; 
B. lactis aerogenes in leucocyte-rich sediment. 
B. lactis aerogenes in whole raw milk 
B. lactis aerogenes in sterilized milk (control) 
Original nailk 
42.000 
5, 400 
36.000 
19 
740 ' 
33 I 92 
a 6 360, 000 
I 
42 I 
1 
“ Innumerable. 
6 About. 
This table also shows the effect of shaking the milk in breaking up 
bacterial clusters. 
