RELATION OF ANAPHYLAXIS TO INFECTIOUS DISEASES 605 



ever, instead of being from eight to twelve days, is now from three to 

 seven, a fact readily explained on the basis that a cell that has once been 

 stimulated to active antibody formation will subsequently respond to 

 the same stimulus with increased activity. This has been called by 

 von Pirquet the accelerated reaction. 



Group III : The reaction appears immediately. If the first injection 

 of horse serum or infection is followed by actual disease or vaccination, 

 the reinjection or reinfection is acquired at a time when the antibodies 

 are present in the circulation in considerable amount, a reaction will 

 occur either immediately or within the first twenty-four hours. This 

 reaction may be quite virulent in intensity, although it is shorter in 

 duration than when it occurs in the first group, von Pirquet speaks 

 of this as the immediate reaction. It is to be observed in cases of serum 

 sickness where the symptoms develop almost immediately following an 

 injection of serum months and even years after a previous injection; 

 it also occurs in cowpox vaccination, where a local reaction takes place 

 very quickly and soon disappears after a previous attack of smallpox 

 or vaccination. 



If the antibodies are present in lesser amounts, the reaction may occur 

 in from the second to the fourth day; this is called the torpid early 

 reaction. 



At the time of the second injection of serum or reinfection with bac- 

 teria a small amount of antibody may still be present; this will give an 

 immediate though mild reaction, and is not enough to neutralize the 

 total amount of foreign protein introduced. A portion of the latter, 

 therefore, will result in the production of an additional amount of anti- 

 body, which occurs in an accelerated manner, and coming in contact 

 with some of the free antigen, gives rise to the accelerated reaction. 

 Hence we may have an immediate, followed by an accelerated, reaction. 



To illustrate these principles, von Pirquet names vaccinia as an 

 example of an acute infection in which the processes may be observed 

 on the skin. As the result of vaccination a colony of microorganisms 

 is formed on the skin. For the first two days the local response is 

 evidently traumatic in character. After the third or fourth day the 

 specific reaction sets in, i^i the form of a small papular elevation sur- 

 rounded by a small areola due to the local action of toxins or protein 

 poison from disintegrated microorganisms. By the eighth day a 

 vesicle has formed, and from its contents new colonies can be grown on 

 thousands of other arms. But one or two days later the ferment-like 



