Spores 
Dust 
116 HOUSEHOLD BACTERIOLOGY 
minutes. This destroys the pathogenic and lactic acid 
bacteria. The milk is then safe, that is, does not carry 
disease germs, and will keep longer than ordinary 
milk, but will in time sour because other germs gain 
access to it. 
Properly Pasteurized milk retains the natural flavor 
and its digestibility is more nearly normal than that 
of milk which has been sterilized. 
Because certain species of bacteria form spores 
which are very resistant to the ordinary methods of 
sterilization, it is necessary to repeat the process to 
ensure success. This repeated boiling for three suc¬ 
cessive days is known as Intermittent Sterilization. 
Infected material which would be harmed by thor¬ 
ough sterilization should be destroyed by fire when¬ 
ever possible. It should never be allowed to become 
dry and thereby add its infectious matter to dust. 
The experiments outlined in the text should be per¬ 
formed as far as possible. The whole lesson will be 
far more interesting if observation of them precedes 
the book study. 
The questions should stimulate the application of 
all principles suggested in the text and, wherever pos¬ 
sible, be answered after actual observation of practice 
based on those principles. 
A further knowledge of the whole subject of the 
micro-organisms included in the science of bacteriol¬ 
ogy may be gained by reading the small but interesting 
books named in the bibliography. 
