VACCINATION AGAINST SMALL-POX. 25 



"ontrol animals always die within twenty-four hours, as in previous experiment, on 

 injection of 1/4 of a loopful. 



From experiment with guinea-pig i, it can be learned, that by gradual increase of 

 the immunizing dose, a state of immunity is reached which can overcome an infection 

 produced by a high multiple of the dosis letalis. 



Experiment 2 and 3 prove that even a single preliminary injection suffices to prevent 

 the death of an animal upon subsequent receipt of the lethal dose of the same bacteria; 

 but that this single inoculation is not sufficient to prepare the organism against a very 

 severe future infection. The attained immunity is therefore only relative, not absolute. 



Analogously it is possible to immunize by subcutaneous and intra- 

 venous injections. The latter method is usually the one of choice when 

 half parasites are employed, as the highest and quickest grade of immunity 

 is thus reached. It carries with it, however, the greatest danger and fre- 

 quently results in death to the animal. 



The method of immunization with small doses of living, fully virulent 

 bacteria, has thus far been made use of only in animals. In man this 

 experience has not been carried into effect. It is feared that the bacteria may 

 increase very rapidly and give rise to severe disturbances. The method has 

 therefore been altered and instead of using virulent material for immu- 

 nization, only a weakly infectious or attenuated virus is employed. 



Vaccination against Small-pox. 



This is the best known example of active prophylactic 

 immunization. To Jenner belongs the credit of having been 

 the first one to apply this principle. Vaccination against 

 small-pox consists in inoculation of an attenuated form of 

 small-pox germs, the diminution in virulence being brought about by pass- 

 age through the body of a calf, a less susceptible animal than man. The 

 vesicles formed on the vaccinated person contain these attenuated germs. 

 This lymph can be used for the inoculation of other individuals, as the 

 germs do not regain their virulence by repassage through man. 



Inasmuch as it is not within the scope of this book to go into the details 

 of the preparation of the lymph or the technique of vaccination, a brief 

 survey of the benefits of vaccination will amply suffice and this may be seen 

 from the table hereunto appended. 



The mortality from small-pox per 100,000 population was in the year 



1862-1876 1882-1896 



in Prussia and Bavaria. 51.6 0.7 



in Austria 75.2 38.6 



in Belgium 79. 5 18. 2 



in England 25.3 2.9 



in Sweden 26.9 0.5 



This method of immunizing against a virulent virus by inoculating with an 

 attenuated form of the same, is known as Jennerization. Pasteur recognized 

 that this method had general application and similarly used attenuated but 



