CHAPTER X 



PHENOMENA FOLLOWING ACTIVE 

 IMMUNIZATION BY VACCINES 



The immediate result consequent upon a suitable dose of 

 vaccine injected into an animal is a fall in the amount of 

 opsonin present in the serum, apparently due to the 

 gathering up of most of the available opsonin to the bodies 

 of the bacteria introduced. This fall in the index is called 

 the " negative phase/' and occupies a period of from twelve 

 to thirty-six hours usually ; if the dose is very large it may 

 last for days, if very small it may be eliminated altogether. 

 With this fall of the index there is usually a rise in tempera- 

 ture ; the pulse may be slightly quickened, and there may be 

 a slight constitutional disturbance, but in the majority of 

 cases there are no appreciable disturbances. When one is 

 dealing with a local lesion, such as quittor, poll-evil, fistula, 

 etc., an increase in the quantity of the discharge will be 

 noticed, the parts become more swollen, and the animal 

 evinces symptoms of increased pain locally. These phe- 

 nomena usually last not longer than twenty-four hours, and 

 are replaced by a return to a more normal condition ; the 

 pulse-beat becomes less, also the temperature, the discharge 

 lessens, and the animal is brighter. We have now entered 

 upon the positive phase. This is due to the stimulus given 

 by the vaccine ; fresh supplies of opsonin are elaborated, 

 during which the opsonic index rises, usually taking a day 

 or two, when the maximum is reached, and a condition is 

 now established which may remain for a day or two, and 

 is called the " phase of increased resistance." 



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