The Protection of Health 593 



utterly adverse conditions in the organism to which it is trans- 

 ferred and it will be unable therefore to grow. Second, it may 

 grow for a time, but be unable to produce or throw off the 

 poisonous substances or toxins, which constitute the principal 

 danger to the body. Third, the germ may grow, multiplying 

 and evolving the toxins which endanger health, but these may 

 be neutralized by natural antitoxins and thus fail to cause the 

 disease. The individual thus infected may experience no 

 interruption of function of an organ or lowering of the generaT 

 health. The mere introduction into the human system of the 

 infective microbe does not, therefore, necessarily mean disease- 

 The microbe must develop, multiplying and evolving toxins, 

 and these must act injuriously upon the body or cause the 

 disease characteristic of the infective organism. 



292. Prevention of infection. The following measures and 

 precautions are suggested for the control and prevention of the 

 transmission of disease-causing microbes. 



I. Artificial immunity. The most effective preventive of 

 the spread of disease would be to render immune all individuals, 

 or at least all who are likely to be exposed to infection. This 

 would block completely and promptly the transmission of dis- 

 ease by creating conditions making it impossible. Modern 

 science in investigating the conditions upon which health and 

 disease depend has discovered so far ways and means of im- 

 munizing against only a few diseases. 



1. Vaccines. Artificial immunity is produced by vaccination 

 or inoculation by hypodermic injection. Vaccination gives 

 active artificial immunity. It is usually the introduction into 

 the blood through a cut or abrasion of the skin of a modified or 

 weakened virus that has been developed in the blood of another 

 person or an animal infected with the disease. The first result 

 of vaccination is the development of a very mild type of the 

 disease, in which are produced by the bodily cells such sub- 

 stances as render the individual actively immune for a con- 

 siderable period of time. Vaccination is extensively practiced 



