n6 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. 



spores 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 Sterilisation. 

 Dust 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. 



