456 Our Surroundings 



he does not catch it. Immunity may be either natural or acquired. 

 It is said to be natural when it is inherited. It sometimes happens 

 that a person does not become ill during an epidemic though all 

 other members of his family are stricken. Such a person has 

 natural immunity. 



Immunity is acquired when it results from some treatment 

 that counteracts the effect of the poison produced by the germs 

 in the body. With certain diseases immunity from a second 

 attack is gained by having the disease itself. Some condition 

 is developed in the system, as a result of having the disease, that 

 makes it impossible for the germs that produce it ever to thrive 

 again in the body. Smallpox is such a disease. It is not known 

 whether smallpox is caused by bacteria or by protozoa. The 

 first method ever used to produce immunity from illness was 

 employed to lessen the effects of smallpox. It is commonly called 

 vaccination. 



Vaccination. Vaccination was discovered in 1796 by Dr. 

 Edward Jenner, an English physician. It consists in introducing 

 germs of cowpox into the system through a slight cut in the 

 skin. The cowpox germs are obtained from the sores on the 

 skin of a healthy calf, caused by vaccinating it with smallpox 

 germs. These cowpox germs, called virus, produce a mild form 

 of the disease and render the patient immune from an attack of 

 smallpox for several years. Previous to this discovery, thou- 

 sands of persons suffered from the dire ravages of smallpox 

 which caused more loss of human life than tuberculosis now 

 causes. 



In the case of a smallpox epidemic general vaccination is the 

 only means of stamping out the disease. Its use should always 

 be advocated, and the prejudice against it in some sections should 

 be overcome. Serious results that sometimes occur from vaccina- 

 tion are usually traceable to infections from germs other than those 

 of the pure vaccine. Such infection should be avoided by having 

 the vaccination performed only by a reliable physician who uses 

 virus that has the guarantee of government inspection in its 

 preparation, and who will give expert advice in regard to the 

 care of the wound made in the skin. 



