RST 1, | On Variation and Adaptation in Bacteria. 557 
On the other hand it is apparent that the organisms did not always respond 
very readily to changed environment in my experiments, and little or nothing 
is at present known of the conditions which determine such response. 
As regards the investigation of the practical problems of pathogenicity 
and virulence it would seem more appropriate to employ media of known 
and definite composition instead of media based upon material so indefinite 
as meat extract, and to use proteins and protein derivatives as test substances 
rather than carbohydrates, alcohols, and glucosides. 
Conclusions. 
1. The reactions of any given strain of streptococcus in Gordon’s media 
vary considerably under the conditions of ordinary laboratory cultivation, and 
by suitable manipulation of the culture media they can readily be made to 
vary very greatly. 
2. The results obtained entirely oppose the view that these reactions 
afford a means of distinguishing fixed and definite varieties among strepto- 
cocci isolated from the human subject. 
3. Such differences as are observed are of a temporary and accidental 
character, and are not in any sense specific, though they may perhaps afford 
some evidence of the natural habitat or previous environment of the 
organisms concerned. 
REFERENCES. 
1. M. H. Gordon, “ Report on some Characters by which various Streptococci and 
Staphylococci may be Differentiated and Identified,” ‘Reports Med. Officer Local 
Gov. Board,’ 1905, p. 388. 
2. A. C. Houston, “ Report on the Bacteriological Examination of (1) the Normal Stools 
of Healthy Persons ; (2) the Intestinal Contents of Sea-fowl and Fish; and (3) 
Certain of our Public Water Supplies,” ‘Reports Med. Officer Local Gov. Board,’ 
1905, p. 472. 
3. Andrews and Horder, “A Study of the Streptococci pathogenic for Man,” ‘ Lancet,’ 
1906, II, pp. 708, 775, 852. 
4, Marmorek, ‘Die Arteinheit der fiir den Menschen pathogenen Streptokokken,” 
‘Berliner Klin. Wochenschr.,’ 1902, vol. 39, p. 299. 
5. Ainley Walker and Ryffel, ‘‘The Pathology of Acute Rheumatism and Allied 
Conditions,” ‘ Brit. Med. Journ.,’ 1903, II, p. 659. 
6. Dreyer and FitzGerald, “The Unreliability of the Neutral Red Method as generally 
employed for the Differentiation of B. typhosus and B. coli,’ ‘Festskrift to 
Celebrate the Inauguration of the Danish State Serum Institute, Copenhagen,’ 
1902. 
7. Twort, “The Fermentation of Glucosides by Bacteria of the Typhoid-coli Group and 
the Acquisition of New Fermenting Powers by &. dysenterte and other Micro- 
organisms,” ‘ Roy. Soc. Proc.,’ 1907, B, vol. 79, p. 329. 
SO el XO bly ——B, ZS 
