THE BACTERIOLOGY OF ICE CREAM 191 
water should be circulated or the freezer slowly cooled in 
some other way before the cold brine is circulated. 
Employees. The direct contamination of dairy products 
from persons is especially undesirable because of the possibility 
of the introduction of pathogenic bacteria in this way. The 
real danger from employees is shown by several typhoid epi- 
demics in which the ice cream causing the infection was con- 
taminated by carriers coming in contact with the material 
during the manufacturing process. The handling of the cream 
after pasteurization should be done under the most careful 
conditions, as should also the handling of the materials that 
are not heated at all. 
CHANGES IN THE Numpers or Bacrerta DuriIna FREEZING, 
HaRrDENING, AND HoLpING 
The changes in the numbers of bacteria during the freezing, 
hardening and holding of the ice cream are of considerable 
importance if bacterial standards for this product are to be 
employed. 
In the modern ice cream freezers, the ice cream mix is sub- 
jected to rather violent agitation in addition to having its 
temperature brought down below the freezing point of water 
and it would be expected that significant changes in the num- 
bers of bacteria, as determined by the plate method, might 
occur. The lowering of the temperature would be expected 
to destroy certain of the bacteria while the agitation would 
be expected to break up the clumps of bacteria that might be 
present. The Iowa Agricultural Experiment Station’? com- 
pared the bacterial content, as determined by the plate method, 
of the ice cream mix and the frozen ice cream in 51 cases. In 
2 cases (4 per cent) there was no change; in 6 cases (11.8 per 
cent) the freezing lowered the count, the decrease varying 
from 2 to 31 per cent (Av. 13.0 per cent) while in 43 cases 
(84.8 per cent) it increased the count from 2 to 227 per cent 
(Ay. 46.3 per cent). A few representative comparisons follow : 
144 Unpublished data. 
