312 THE STREPTOCOCCUS-PNEUMOCOCCUS GROUP 
in man or animal as the struggle between host and invader is extended 
in time. 
Prophylaxis. — General surgical aseptic methods. Autogenous vac- 
cines have been extensively used in streptococcus infections,' but 
with less favorable results than has attended the use of autogenous 
staphylococcus vaccines. The possibility of streptococcus carriers, 
particularly those harboring Streptococcus pyogenes (Streptococcus 
hemolyticus) should be borne in mind. This is particularly import- 
ant in hospital wards where measles cases are being cared for. 
The Streptococcus Einheit or Vielheit.— Considerable discussion 
has arisen concerning the unity or the plurality of types included 
within the organism known as Streptococcus pyogenes. Marmorek^ 
and others have stoutly maintained the Einheit theory. Considerable 
evidence in favor of this view was advanced by Koch and Petruschky/ 
who showed that a streptococcus obtained from a fatal puerperal sep- 
sis caused erysipelas in a rabbit when it was injected subcutaneously, 
peritonitis when injected intraperitoneally, and septicemia when 
introduced intravenously. The organisms freshly isolated caused a 
rapidly fatal septicemia when introduced through the blood stream, 
but the virulence was gradually lost following cultivation on artificial 
media; the septicemic phenomena diminished in intensity and there 
was evidence of a localization of the organisms. Their conclusions 
were that the type of lesion produced by Streptococcus pyogenes 
depended largely upon the virulence of the culture, the tissue invaded 
and the number of organisms. With a comparatively slight loss in 
virulence the endocardium appeared to be somewhat more frequently 
the site of the focal infection; with a greater loss of virulence, the joints. 
It must be remembered in this connection that the virulence of a 
streptococcus for man does not necessarily determine the virulence for 
animals. 
It is possible to raise the virulence of streptococci very materially 
by artificially creating portals of entry and of escape which are not 
usually available to the streptococcus. This is accomplished by 
passage through experimental animals. By passage it is possible 
to reproduce with considerable accuracy the various reactions men- 
tioned above, depending upon the virulence of the organism, the 
tissue into which the injection is made, and the number of organisms 
introduced. It is also important to remember that an increase in 
virulence for one animal, attained by frequent passages, frequently 
results in a loss, partial or complete, of the Airulence of the organism 
for another animal. Too little is known of the mechanism of viru- 
lence, however, to place a final interpretation upon the biological 
significance of changes in pathogenic powers. 
1 Boughton: Jour. Infcc. Dis., 1910, 7, 99, 111. Weaver: Trans. Assn. Am. Phys., 
1910. 
2 Berl. klin. WVhnschr., 1902, 39, 299. 
' Loc. eit. 
