594 Introduction to the Study of Science 



for such diseases as smallpox and typhoid fever, and may on 

 occasion be extended to cholera and bubonic plague for men, 

 and anthrax in the case of animals. 



2. Antitoxins. The injection of antitoxins and of bacterial 

 substances in the form of serum has become quite general in 

 late years. Antitoxins are employed especially in diphtheria 

 and tetanus. The antitoxin when injected is diffused through 

 the circulatory system where it neutralizes toxins that may be 

 produced by the bacteria. It does not stimulate the bodily 

 cells to produce antitoxins or increase the natural defenses, 

 and can give, therefore, only temporary protection. It acts 

 primarily as a curative or therapeutic agent, and incidentally 

 gives a temporary and passive immunity to the specific disease. 



II. Control of disease germs in the body. Natural immunity 

 is greatly limited, and artificial immunity can be acquired 

 through vaccines and antitoxins for only a few infective dis- 

 eases. This makes it necessary to find other ways for pre- 

 venting the spread of infection to the healthy. A fact of 

 fundamental importance is that pathogenic germs multiply and 

 produce their toxins in the living body of a patient. They 

 must, therefore, be destroyed, either at their source of generation 

 or after they leave the patient. Unfortunately, it is not as a 

 general rule possible to destroy by specific treatment the disease 

 germs in the patient except by such means as would destroy the 

 patient. In only a few diseases, such as malaria, is destruction 

 of the parasites in the patient possible. The primary aim of 

 medical practice is, therefore, to assist the natural energies to 

 overcome the disease and to restore health. It aims only in- 

 cidentally to destroy the pathogenic organisms. 



In the case of certain diseases, as typhoid fever and diph- 

 theria, the pathogenic germs continue to flourish in the body 

 of the recovered patient, some being expelled from time to time 

 in such ways as may expose others to infection. An individual 

 who may be such an incubator and carrier of disease germs 

 suffers no ill effects, because the toxins produced are neutralized. 



