BACTERIA 141 



soap and water, walls re-papered or calcimined if possible, bedding 

 either sterilized or burned and the room tightly closed and fumi- 

 gated. For this purpose formaldehyde gas is best and may be 

 prepared by burning a formalin candle, boiling a strong solution 

 of formalin, or by adding permanganate of potash crystals to the 

 solution in the proportion of one-half pound of crystals to each 

 pint of formaldehyde. While not -so efficient, and also likely to 

 bleach colored furniture, burning sulphur produces a gas which is 

 a useful disinfectant. One or the other of these substances should 

 always be used in rooms where an infectious disease has occurred. 



Germs, both bacteria and animal forms, are mostly killed at boil- 

 ing temperature. Drying checks their growth and direct sunlight 

 destroys them rapidly. When we cook our foods, we not only make 

 them more digestible and attractive, but sterilize them as well. 

 Milk may be freed of the most dangerous bacteria by pasteuriza- 

 tion, which means heating to a temperature of from 140 to 150 F. 

 for a period of 30 minutes. After pasteurizing it must be quickly 

 cooled and kept closed and cool, or other germs will find entrance. 



This brings us to another way in which bacteria do harm to man: 

 they attack his foods, causing them to sour, ferment, or decay. 

 Cooking and canning are two ways which have been mentioned 

 of preserving food from bacteria. Meats are protected by canning, 

 cold storage, salting, smoking, pickling, etc. ; fruits and vegetables 

 may be canned, dried, or pickled in vinegar and spices which are 

 really antiseptics. Other more active antiseptics have been used 

 to preserve foods, such as borax, formalin, salicylic acid and ben- 

 zoate of soda, but, while they kill the bacteria, they also harm the 

 person using the foods, and so have mostly been forbidden by law. 



Development of Bacteriology. Our knowledge of the action 

 of bacteria dates back only about forty years, but during this time 

 great headway has been made in their control. Pasteur discovered 

 the relation of bacteria to fermentation about 1860 but it was not 

 until 1880 that their connection with human disease was established. 

 Pasteur's great work against rabies mad dog poison was 

 done about 1885 and now only one per cent of the victims die, 

 instead of practically every one, as formerly. In 1894 Von Behring 



