DIPHTHERIA 239 



of newborns, nearly 90 per cent, of adults, and from 50 to 60 per 

 cent, of children. It has accordingly been suggested that prophy- 

 lactic antitoxin injections could be dispensed with in many cases, if 

 it were possible to determine by some relatively simple procedure 

 whether the individual in question was naturally protected or not. 

 This seems to have been accomplished by Lowenstein, Michiels, and 

 Schick. These investigators have pointed out that the intracuta- 

 neous injection of very small doses of diphtheria toxin produces a 

 specific skin reaction in individuals whose blood-serum does not 

 contain any antitoxin. It is hence suggested to resort to this test 

 whenever the prophylactic use of diphtheria antitoxin comes into 

 question and to inject only those who give a positive reaction. To 

 this end -^ of a single lethal dose for 250 gm. guinea-pig is recom- 

 mended, the volume injected being preferably not more than 0.1 

 c.c. For example: supposing the lethal dose for 250 gm. guinea-pig 

 to be 0.005 gm., the amount to be injected could be 0.1 c.c. of a 

 1 to 1000 dilution of the original material. This quantity is intro- 

 duced intracutaneously with a very thin needle, the aperture of 

 which is directed upward. The resultant reaction, if positive, 

 resembles a tuberculin reaction. It appears after the traumatic 

 reaction has faded away, viz., after from four to eight hours, and 

 reaches its maximum intensity after forty-eight hours, covering an 

 area of from 10 to 25 mm. in diameter. A positive reaction at 

 the expiration of twenty-four (rarely forty-eight) hours may be 

 regarded as indicating an absence of natural antitoxin and hence as 

 an indication for a prophylactic injection. A negative reaction, on 

 the other hand, may usually be regarded as indicating a sufficient 

 degree of natural protection excepting in about 10 per cent, of 

 newborns and severely cachectic children, in which the power of 

 reaction on the part of the skin is at a low level. 



These observations should prove of special value when large 

 bodies of individuals are to be examined and eventually protected, 

 as a great deal of labor would thus be obviated and direct informa- 

 tion afforded within twenty-four hours as to who should and should 

 not be injected, bearing in mind that it is probably only the naturally 

 unprotected individual who is really in danger. 



Since passive immunization with diphtheria antitoxin only protects 

 the injected individual for a relatively short time, it has been sug- 

 gested to combine active immunization with the administration of 



