fatal disease.) These bacteria he cultured on suitable 

 chemical media, and animals inoculated with bacteria 

 from these cultures developed the respective diseases, 

 proving that the bacteria were the actual causes of the 

 diseases concerned. Since healthy animals often recover 

 from a disease , it was evident that their bodies had mecha- 

 nisms for killing invading bacteria: also, since a first 

 attack of a disease usually rendered a second attack of 

 the same disease on the same animal less severe than the 

 original attack, or prevented further attacks altogether, it 

 appeared that the bacteria themselves stimulated the body 

 to produce something which could later render the par- 

 ticular bacterium inactive. Pasteur concluded that the 

 artificial inoculation of bacteria into an animal would 

 produce an antitoxin in its blood, which could be extracted 

 by separating the blood serum (blood cells and bacteria 

 removed) from the blood, and which should confer immu- 

 nity to the particular disease on animals into which it 

 was inoculated. He carried out these experiments and was 

 delighted to find that the results agreed with his theory of 

 immunization outlined. 



Today antitoxins (effective against bacterial toxins or 

 poisons), or antisera (acting against bacteria themselves), 

 have been made for many bacterial diseases, thus making 

 actual or possible the elimination of e.g. typhoid, cholera, 

 etc., when used in conjunction with satisfactory standards 

 of hygiene to prevent the spread of disease. We can feel 

 fairly confident today that not only bacterial, but also virus- 

 caused, diseases can be virtually wiped out by means of 

 this technique of inoculation. 



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