STREPTOCOCCUS PYOGENES. 491 
Is Protection Afforded by the Same Serum Against All 
Varieties of Streptococci ? 
We have tested the protective value of one serum 
against five streptococci. First, the streptococcus given 
us by Marmorek, which was obtained from a case of 
angina complicating scarlet fever. Its virulence is now 
such, after having passed through hundreds of rabbits, 
that 0.000001 ¢.c. is the average fatal dose. Second, 
a streptococcus obtained from a case of erysipelas in 
England. Its virulence is 0.00001 c.c. on the average. 
Third, a streptococcus obtained from a case of cellu- 
litis a few weeks ago, its virulence being about 6 c.c. 
Fourth, a streptococcus sent me by Theobald Smith. 
Its virulence is such that 0.1 ¢.c. is the average fatal 
dose. Fifth, another culture sent me by Smith, which 
grew in short chains and was obtained from milk; its 
virulence was similar to No. 4. 
Against the first three streptococci derived from three 
different varieties of infection existing in three different 
countries the serum produced in the horse by the strep- 
tococcus from England had nearly the same value. 
Against the latter two streptococci, as well as against 
a pneumococcus, which in ordinary cultures looks like 
a streptococcus, the serum had no effect. 
The results published by others must also be taken 
to prove that a serum which protects from infection 
with one streptococcus may fail against others; but, 
taking all together, they indicate that the majority of 
streptococci met with in practice will be influenced by 
the same serum. Many more streptococci, however, 
must be obtained from human infections and tested 
before we can be certain of this. Those obtained from 
