VACCINATION. 



In smallpox we do not know the etiological 

 agent, therefore we cannot produce a specific 

 serum but must use the whole virus in the form 

 of a vaccine. 



Protective inoculation, or in other words, 

 vaccination is now-a-days used to protect 

 against diseases other than smallpox and with 

 equal propriety. Attenuated, or killed virus of 

 a disease is inoculated and resistance to an in- Diseases 

 fection is established. Hydrophobia is treated ™ Which 

 by inoculation as is also typhoid fever, plague. Is Used, 

 cholera, dysentery, etc. Protection (im- 

 munity) is not established immediately. We 

 are familiar with the fact that in vaccination 

 against smallpox infection, several days elapse 

 before immunity is gained. This is also true of 

 vaccination or inoculation against other dis- 

 eases. Wright of "opsonic theory" fame, calls 

 this period between vaccination and the time 

 when immunity is gained "the negative phase." phf^e!^^ 

 The period following the formation of protec- 

 tive properties in the subject treated he calls 

 "the positive phase." The length of time of the ^'^^^'^ 

 negative phase is dependent upon the nature 

 and the quantity of the virus injected. We do 

 not know the nature of all protective products. 

 If the micro-organism which causes the disease 

 is unknown it is not easy to determine what 

 protective products are formed by inoculation. 



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