464 INFECTION AND RESISTANCE 



The Homer method has been recently used by clinicians for the 

 determination of the presence of free toxin or antitoxin in the circu- 

 lating blood of patients suffering or convalescent from diphtheria. 

 Homer himself suggested this, since his method is adapted to the 

 determination of extremely slight amounts of either substance. A 

 recent study by Harriehausen and Wirth 34 illustrates the results 

 obtained in such tests, formal human serum injected intracuta- 

 neously into guinea pigs never caused necrosis. Neither did the 

 similar injection of the sera of children suffering from varicella and 

 other diseases. Of twelve children suffering from diphtheria, how- 

 ever, serum taken before the administration of antitoxin caused 

 necrosis upon intracutaneous injection into guinea pigs, in every 

 case. In spite of the administration of antitoxin, toxin was demon- 

 strable in the blood in five cases as long as the 35th day. Of ten 

 cases of post-diphtheritic paralysis, toxin was demonstrated in the 

 blood of five. 



Since this method of determining antitoxin values in the blood 

 of human beings is of considerable importance and may have much 

 practical value, it may be useful to insert an example of such an 

 application of this method as used by Hahn 35 in a series of investi- 

 gations mentioned elsewhere. 



The standard toxin was obtained from Marburg. In a series 

 of guinea pigs a determination was made of the smallest quantity of 

 this standard poison which would produce just noticeable necrosis 

 of the skin if injected into the pig intracutaneously, together with 

 1/2, 000th of a unit of a standard antitoxin. The toxin and antitoxin 

 were left together for 24 hours before injection, 3 hours in the incu- 

 bator, and 21 hours in the refrigerator. 



When this quantity of the antitoxin had been determined, it 

 could be used in similar experiments and similarly mixed with vary- 

 ing amounts of the patient's serum. The amount of antitoxin pres- 

 ent in such serum could then be easily computed. For, let us sup- 

 pose that this amount of toxin, together with 1/5 00th of a c. c. of 

 the serum injected intracutaneously into the guinea pig, gave the 

 same amount of necrosis in the same time as the identical quantity 

 of the toxin, together with 1/2, 000th of a standard unit. Then 

 l/500th of a patient's serum was equivalent to 1/2, 000th of a stand- 

 ard unit, and the patient's serum would contain 0.25 of a unit 

 per cubic centimeter. 



Michiels and Schick 36 have carried out intracutaneous reactions 

 with diphtheria toxin directly upon the human body to determine 

 whether or not diphtheria immunity was present. They injected 

 0.1 c. c. of a 1 to 1,000 dilution of toxin and claim that a positive 



34 Harriehausen and Wirth. Zeitschr. f. Kinderlieilkunde, Vol. 7, 1913. 



35 Hahn. Deutsche med. Woch., Vol. 38, No. 29, 1912. 



36 Michiels and Schick. Zeitschr. f. Kinderheilkunde, Vol. 5, 1912. 



