100 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 Menna, 

 devised a simple skin reaction by which to determine 

 whether or not an individual was susceptible to diphtheria 

 infection; i. e., to determine whether the individual had 

 or had not diphtheria antitoxin in the blood. It has been 

 demonstrated that over 90 per cent, of newborn infants 

 have antitoxin in their blood. At one year of age only 

 about 60 per cent, remain immune, while between five 

 and fifteen years of age about 50 per cent, are immune. 

 After this the proportion of immune individuals rises so 

 that between twenty and forty years o^'er 75 per cent, 

 are immune to diphtheria. 



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 sus- 

 ceptible there is practically no reaction. The Schick test 

 is being used extensively to determine the need of actively 

 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 bodv'. 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. 



