260 BACTERIA AND DISEASE 



last named is one of the most powerful as well as the most dan- 

 gerous to use. As it attacks metal, it should not be used in a metal 

 pail or dish. It is commonly put up in tablets which are mixed 

 to form a 1 to 1000 solution. Care must be taken of both the 

 tablets and the solution to avoid a possible accidental poisoning. 

 Formaldeh^^de in solution, called formalin, is used as a disin- 

 fectant. When vaporized, it sets free an intensely pungent gas 

 which is sometimes used for disinfecting the sick room after the 

 patient has been removed. 



Carbolic acid is an excellent disinfectant although it will not 

 kill spores of bacteria. If used in a solution of about 1 part to 25 



of water, it will not burn the skin. It 

 is of particular value in disinfecting skin 

 wounds. Lysol is another excellent 

 disinfectant, because it can be used 

 with soap. Iodine is often used as a 

 skin disinfectant and in open wounds. 

 Chloride of lime is an old-time but good 

 disinfectant ; it also is a deodorant. 

 One of the newest disinfectants is mer- 

 curochrome. 



A single cell scraped from the ^ . ^x. mi ±. 



roof of the mouth and highly Bacteria cause Disease. — The most 

 magnified. The little dots are harmful bacteria are those which cause 



bacteria, most of which are ,. ,• i i i • i i-t j • 



harmless. diseases 01 plants and animals. Certain 



diseases of plants — blights, rots, and 

 wilts — are of bacterial nature. These do much damage annually 

 to fruits and other parts of growing plants useful to man as food. 

 But by far the most harmful are the bacteria which cause many 

 diseases in man. They accomplish this by becoming parasites in 

 the human body. Millions upon millions of bacteria exist in the 

 human body at all times — in the mouth, on the teeth, and espe- 

 cially in the lower part of the food tube. Some in the food tube 

 are believed to be useful, some harmless, and some harmful ; others 

 in the mouth cause decay of the teeth, while a few species may cause 

 disease. Such disease-causing bacteria are called pathogen'ic. 



It is known that bacteria, like other living things, take in food, 

 form organic wastes within their own bodies, and give off some 

 of them. These wastes, called toxins, are poisonous to the host 



