THE DIPHTHERIA BACILLUS 433 
in the toxin-antitoxin mixture. General symptoms and fever to 103° 
to 104° F. are observed in a few cases. This direct method of inducing 
immunity has been used rather widely to induce active immunity to 
diphtheria. The immunity thus induced lasts a year or more. It 
must be remembered that a not inconsiderable porportion of persons 
thus immunized are simultaneously sensitized to horse serum. The 
use of Ramon's anatoxin^ promises to supplant the more dangerous 
toxin-antitoxin mixture. 
The Schick i?eadio/i.— Available evidence indicates that immunity 
to infection with the diphtheria bacillus depends largely upon the 
antitoxin content of the blood, and systematic studies of the anti- 
toxin content of the blood of infants, children and adults by Schick,- 
Park, Zingher and Serota,^ Park and Zingher,^ Kolmer and Moshage,^ 
Bundersen,'' and Moody^ indicate that a large percentage— nearly 80 
per cent of young infants, 50 per cent of children, and nearly 90 per 
cent of adults— exhibit sufficient antitoxin to protect them against 
the disease. The demonstration of antitoxin in the blood has been 
simplified greatl>' by Schick, and modified somewhat by Park.^ It 
is made in the following manner: an amount of diphtheria toxin 
equivalent to one-fiftieth the minimal fatal dose for a guinea-pig is 
made up to a volume of 0.2 cc. in sterile salt solution and is injected 
subcutaneously, or preferably intracutaneously, in the flexor surface 
of the forearm. Immediately the skin is raised somewhat as the fluid 
enters the tissues. The reaction elicited depends upon the antitoxin 
content of the blood. A positive reaction, indicating that antitoxin 
is absent, or present in minimal amounts, appears within twenty-four 
hours as a circumscribed area of redness and a more diffuse area of 
induration measuring from ^ inch to more than 1 inch in diameter. 
The maximum reaction appears within forty-eight hours and disappears 
within a week. The blood of a patient reacting in this manner contains 
less than gV unit of antitoxin per cc. A fainter reaction is frequently 
exhibited, which is interpreted to mean that the antitoxin content of the 
blood lies approximately between 4^,^ and jV antitoxin unit per cc. If 
the antitoxin content is at least 2V ^^it per cc, the reaction is negative; 
only a slight reaction results due to the wound itself. 
Practically, it has been found that individuals giving a negative 
reaction possess sufficient antitoxin to protect them from infection; 
nurses, doctors, ward orderlies, and patients who react negatively do 
not need to be immunized with antitoxin if they have been, or are, 
exposed to the infection. Persons gi^■ing a mild or severe reaction 
should be immunized with prophylactic doses of antitoxin. 
1 Ann. Inst. Pasteur, 1925, 39, 1; 1926, 40, 1; also Glenny, Hopkins and Pope: Jour. 
Pathol, and Banteriol., 1924, 27, 261. Weinberg and Gay: Compt. rend. .Soc. hiol., 
1924, 91, 1140. 
2 Munehen. med. Wphnschr., 191:^, 40, 260S. ^ Areh. Pediatrics, .July, 1914. 
* Proc. New York Path. 8oc., N. 8., 1914, 14, 151. 
5 Am. Jour. Dis. Child., 1915, p. 189. 
6 .Jour. Am. Med. Assn., 1915, 64, 1203. " Ibid., 1915, 64, 1206. 
» Loc. cit. 
28 
