193 PATHOGENIC BACTERIA. quently transplanted they die. In bouillon they are said to die in five to ten days. On solid media they seem to retain their vegetative and pathogenic powers much longer. They resist drying well. Their growth in arti- ficial media is accompanied by the production of an acid which probably acts destructively upon the bacteria themselves. The Streptococcus pyogenes is generally not very patho- genic for animals. Subcutaneous injections into mice and rabbits are, as a rule, without either general or local manifestations of importance. If, however, an ear of a rabbit is carefully inoculated with a small amount of a pure culture, a small patch resembling erysipelas usually results. The disturbance passes away in a few days and the animal recovers. If, however, the streptococcus is highly virulent, the rabbit dies in from twenty-four hours to six days from a general septicemia. The cocci may be found in large numbers in the heart's blood and in the organs. In less virulent cases minute disseminated abscesses are some- times found. According to Marmorek,1 the virulence can be increased to a remarkable degree by rapid passage through rabbits, and maintained by the use of a culture-medium consist- ing of three parts of human blood-serum and one of bouillon. The blood of the ass, and ascitic and chest fluids may also be used. By these means Marmorek suc- ceeded in intensifying the virulence of his culture to such a degree that one hundred millionth of a c.cm. injected into the ear vein was fatal to a rabbit. Petruschky2 found the virulence of the culture to be well retained if the culture was planted in gelatin, trans- planted every five days, and when grown kept on ice. Hoist3 succeeded in keeping an exceedingly virulent Streptococcus brevis on artificial culture-media for eight 1 Ann. de VInst. Pastettr, Tome ix., No. 7, July 25, 1895, p. 593- 2 Centralbl. fur Bakt. und Parasitenk., Bd. xviii., No. 16, May 4, 1895, p, 551- 3 Ibid., Bd. xtx., No. n, Mar. 21, 1896.