98 APPLIED BACTERIOLOGY FOR NURSES 



injections are spoken of as "immunizing injections"; 

 the dose for this purpose is usually 1000 units. 



Schick Reaction. A few years ago Schick, of Vienna, 

 devised a simple skin reaction by which to determine 

 whether or not an individual was susceptible to diphtheria 

 infection. The test consists in the injection into the skin 

 of a small amount of diphtheria toxin. Within twenty- 

 four to forty-eight hours a marked area of redness and 

 induration develops in those who are susceptible; in those 

 not susceptible there is practically no reaction. The 

 Schick test is being used extensively to determine the need 

 of immunizing children exposed to diphtheria infection. 



When we immunize a person against diphtheria by 

 means of diphtheria antitoxin the immunity conferred 

 lasts only a few weeks. This is because the antitoxin in- 

 jected is horse antitoxin and so is really a foreign substance 

 in the human body. For this reason the plan has recently 

 been adopted of making a person immune against diph- 

 theria by injecting him with diphtheria bacilli and diph- 

 theria toxin, thus causing the body to produce its own 

 antitoxin. This plan, spoken of as active immunization, 

 has been extensively tried by Park and Zingher, and ap- 

 pears to yield excellent results. 



