THE STREPTOCOCCUS GROUP 31.") 
twenty-four hours, at which time it is usually at its height, and is read. 
Less susceptible persons may have an area about 1 cm. in diameter. 
The reaction usually bejiins to fade by the thirty-sixth hour.' It 
should be emphasized that this method of testing; the potency of the 
poison upon susceptible persons is the only one available at present. 
In general the potency of suitable toxic filtrates of scarlet fever strep- 
tococci varies from 500 to 2000 skin doses. - 
This toxic filtrate may also be used for purposes of immimization. 
The Dicks have shown tliat properly graduated and spaced injections 
will render those giving a positive Dick test negative in most instances, 
and usually after three injections. The amounts of filtrate injected 
vary, but an initial amount of 500 skin-test doses, followed by 1000, 
then 2500 skin-test doses is usually employed.^ The duration of the 
immunity thus induced is at least for one year. 
Antitoxic and Antimicrobic Sera.— About the same time the Dicks 
were demonstrating the etiology of scarlet fever, and perfecting their 
technique for immunization, Dochez"* was immunizing experimental 
animals to streptococci he obtained from scarlet fever cases, using 
cylinders of agar thoroughly infected with the organisms for injection. 
By so doing the bacteria were protected from the phagocytes, and thus 
were kept alive for several weeks. In from six to eight months the 
serum of horses thus immunized contained fairly high concentrations 
of antitoxin, and thus could be used therapeutically in the treatment of 
scarlet fever. IVIoser^ seems to have been the first to develop a serum 
for the treatment of scarlet fever, but he had no method for testing 
the potency and it was gradually lost sight of even though some of it, 
in the light of present knowledge, seems to have been effective. The 
discovery of Schultz and Charlton'^ that the serum of a convalescent 
scarlet fever patient, introduced into the skin of an early case, caused 
a blanching, was unavailable to Moser, and thereby frustrated his 
attempts to measure the potency of his preparations. Now, with the 
Schultz-Charlton test, it is possible to measure the neutralizing power of 
streptococcus antiserum, and with this valuable guide, the Dochez 
serum has proved to be of unquestioned value in the treatment of this 
dread disease. It is customary now to measure the potency of the 
antistreptococcus serum in terms of the number of skin-test doses it 
will neutralize. One unit probably will be defined officially as that 
amount of antitoxic serum which will neutralize 100 skin-test doses of 
poison. 
When the case to be treated is a severe one, the serum is injected 
intravenously; when it is a relatively mild case, intramuscular injections 
' Pseudo reactions occasionally occur: the cause is as yet undetermined. See Zinsser: 
Jour. Am. Med. Assn., 1924, 83, 84, 432. 
2 For details of testing see Dick and Dick: Jour. Am. Med. Assn., 1925, 84, 1477. 
» Nesbit: Ibid., p. 805. 
* Proc. Soc. E.xp. Biol, and Med., 1924, 4, 1S4. 
6 Wien. klin. Wchnschr., 1902, 15, 1503. 
« Ztschr. f. Kinderheilk., 1918. 7, 328. ^f^ 
^^ 
