328 



Constant 



A vaccine against tuberculosis has also 

 been given experimentally by the United 

 States Public Health Service to 100,000 

 or more people. The vaccine which was 

 used (called BCG) was originally made 

 in France. Other vaccines have been used 

 but no one can yet say that any of these 

 vaccines will provide complete protec- 

 tion against tuberculosis. 



Influenza vaccines are being experi- 

 mented with and used. And experiments 

 are being carried on with immunization 

 against bubonic plague. Bubonic plague 

 we think is the disease that was called the 

 Black Death and that swept over the 

 whole of Europe in the Middle Ages. 



Passive acquired immunity. In typhoid 

 fever, smallpox, rabies, and the other dis- 

 eases just mentioned, the animal acquires 

 active immunity by the formation of 

 antibodies in its tissues. Late in the last 

 century, another important discovery 

 was made in the fight against diseases. In 

 1892 a pupil of Koch, a German physi- 

 cian by the name of Emil von Behring, 

 gave successful inoculations against diph- 

 theria. His method was difl^erent from 

 that developed by Pasteur, and his object 

 was to find a cure rather than a preven- 

 tion. 



Diphtheria germs enter through the 

 nose or mouth and settle in the throat. 

 Here they produce a painful swelling. 

 The toxins they excrete are carried 

 through the body, causing high fever and 

 distressing symptoms. Emil von Behring 

 knew that the diphtheria germ produces 

 a toxin that enters the blood stream. The 

 tissue cells produce an antitoxin which 

 acts against, or neutralizes, the toxin. 

 Knowing this, Behring decided that some 

 other animal could be made to do the 



Care Is Needed for Health unit vi 



work of producing the antitoxin. This 

 could then be transferred into the human 

 body ready-made and ready for action. 

 His reasoning proved to be correct. Beh- 

 ring raised diphtheria germs in pure cul- 

 ture and injected some into a healthv 

 horse. He was using Pasteur's method of 

 building up active immunit>^ Later he 

 took the antibodies from the horse and 

 injected them into a person. By this 

 method, the human body can be fully 

 armed against diphtheria within a few 

 hours. Behring used the treatment mostly 

 to cure children after they showed symp- 

 toms of the disease; but he also injected 

 the antibodies into a child that had been 

 exposed to the disease but had not yet 

 been taken ill. He found that the anti- 

 bodies could be used both as a cure and 

 as a preventive. 



If used as a cure it is extremely impor- 

 tant that the antitoxin be given as soon 

 as the diagnosis is made and that a com- 

 petent physician be called to make a di- 

 agnosis if diphtheria is suspected. When 

 the antibodies are given as a preventive, 

 the person acquires passive inrunmity. It 

 is called passive because the person's cells 

 remain inactive. Such passive immunity 

 is obtained immediately but lasts only 

 two or three weeks. 



How antitoxin is prepared. A pure cul- 

 ture of the germs is made in broth; tox- 

 ins accumulate in the broth. The bac- 

 teria are filtered out, and the toxin is 

 collected. It is treated with various 

 chemicals to weaken it. It is then called 

 toxoid. This toxoid is injected into a 

 horse. A small amount of toxoid is used 

 for the first inoculations. Then toxin is 

 used. Every five or six days, over a pe- 

 riod of several months, the horse is inoc- 



