INFECTIOUS DISEASES 429 



time they cause the body to produce substances which will 

 prevent the growth of smallpox germs in the person. This 

 method of immunizing the body is called vaccination, from 

 the name of the disease in cattle. It was discovered by 

 an English physician named Edward Jenner. 



It is doubtful if quarantine and attention to hygiene would be sufficient 

 to prevent the spread of smallpox, for mild cases sometimes occur which 

 are not recognized until some one catches the disease in a bad form. 

 Vaccination is an almost sure protection against these unrecognized 

 cases, and very few vaccinated persons who are exposed to severe 

 smallpox take the disease. Every child should be vaccinated before 

 going to school and again a few years later. Objection is often made 

 to vaccination because it has sometimes been followed by severe sick- 

 ness when it has been done with impure vaccine or in a dirty manner. 

 Pure vaccine can now be bought at most drug stores. If it is used in a 

 clean manner, and the vaccinated spot is kept clean, there are no bad 

 results after vaccination. 



747. Lockjaw. Lockjaw ', or tetanus, is caused by a kind 

 of bacteria which grow in a wound. Their toxins poison 

 the nerve cells so as to produce convulsions which usually 

 end in death. The bacteria are often found in the soil of 

 gardens and roads, and reach our flesh through wounds. 

 They cannot grow in the presence of much air, and so they 

 seldom grow in clean, open wounds, but they are likely to 

 grow where they are thrust deep into the flesh, as by dirty 

 nails. They are also likely to grow in wounds made by 

 fireworks on the Fourth of July, for the dead and burned 

 flesh keeps out the air. Lockjaw can usually be prevented 

 by covering all wounds with clean antiseptic dressings. 

 An antitoxin against lockjaw can be bought at drug stores, 

 and should be given soon after a person receives a wound 

 in which there is dirt from soil. 



748. Rabies. Rabies, or hydrophobia, is a deadly form of sick- 

 ness which resembles lockjaw, and is caused by large germs which are 



