254 BACTERIA, YEASTS, AND MOLDS 



as to whether he is careful or careless in handling it. 

 In general it is well not to buy milk from a dirty or 

 careless milkman, for such a man is much more likely 

 to sell milk that is a source of danger. For this reason 

 milk distributed in glass bottles is more reliable than 

 that distributed from metal cans. 3. Practically all of 

 these dangers may be avoided by the use of pasteurized milk, 

 Grade A milk, or certified milk. The latter are higher 

 grades of milk, coming from special farms, and should 

 have a proper certificate or an oflficial grading. They cost 

 more than the ordinary grade, but are safe, and may be 

 given to infants without fear of contagious diseases. In 

 general, then, the first factor to be considered in guard- 

 ing the family from disease through milk is the obtaining 

 of the supply from reliable sources only, even though the 

 price may be higher. This will give a more reliable prod- 

 uct, one that is more valuable as a food and less liable to 

 produce disease. 



But in many households this may not be possible, and 

 the family may be obliged to depend upon the ordinary 

 milk supply without any knowledge of its source. What 

 should be done under these circumstances.? Such milk 

 can be rendered harmless, so far as concerns the diseases 

 referred to, by the processes of pasteurization mentioned on 

 another page. Since milk from an unknown source may 

 be rendered safe for use in this way, it is easy to under- 

 stand why pasteurization has in recent years come to be 

 so widely adopted. The same end is less satisfactorily 

 reached by boiling. 



Every housekeeper will ask, however, whether such a 

 precaution is necessary under ordinary conditions. This 



