BACTERIAL DISEASES 461 



Disinfection. Frequently it becomes necessary to destroy 

 bacteria with chemicals. This process is called disinfection. 

 Although sunlight, dry heat, steam, and electricity kill germs, we 

 commonly apply the term " disinfectant " to such substances as 

 iodine, mercurochrome, potassium permanganate, chloride of lime, 

 carbolic acid, formaldehyde, lysol, and bichloride of mercury. Of 

 these, the last named is one of the most powerful as well as the 

 most dangerous disinfectant 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. 



Formaldehyde in solution, called formalin, is used as a disin- 

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

 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. One of the newest germicides 

 is mercurochrome. It is particularly valuable for wounds and 

 skin bruises in which bacteria might thrive. 



Self-Testing Exercise 



(1) kills bacteria. Canning makes use of the principle 



of (2) . Pasteurization of milk is performed best by heating 



for (3) minutes to a temperature of from (4) to 



(5) F. Harmless preservatives are (6), (7), 



(8), and (9). Antiseptics are used to (10) 



the (11) of (12). Disinfectants are used to 



(13) (14). A germicide (15) all (16). 



PROBLEM II. HOW DO BACTERIA CAUSE DISEASE? 



Bacterial diseases. Bacteria cause many diseases in man. They 

 accomplish this by becoming parasites in the human body. Mil- 

 lions upon millions of bacteria exist in the human body at all times 

 — in the mouth, on the teeth, and especially in the lower part of 



