404 BACTERIA IN CROUPOUS PNEUMONIA. 
rather scanty, almost homogeneous, and semi-transparent. Upon 
potato no development occurs, even in the incubating oven. Milk is 
a favorable culture medium, and the casein is coagulated as a result 
of its presence. 
It ceases to grow on solid media at about 40° C., and in favorable 
liquid media at 42°C. Its thermal death-point, as determined by 
the writer, is 52° C., the time of exposure being ten minutes. It 
loses its vitality in cultures in a comparatively short time—four or 
five days on agar—and is very sensitive to the action of germicidal 
agents. Its pathogenic power also undergoes attenuation very 
quickly when it is cultivated in artificial media, but may be restored 
by passing it through the bodies of susceptible animals. Attenua- 
tion of virulence may also be effected by exposing bouillon cultures 
to a temperature of 42° C. for twenty-four hours, or by five days’ 
exposure to a temperature of 41° C. 
Emmerich reported in 1891 to the Congress of Hygiene and 
Demography in London the results of experiments made by him 
relating to immunity in rabbits and mice. Rabbits were rendered 
immune by the intravenous injection of a very much diluted but 
virulent culture of the micrococcus. The flesh of these immune 
rabbits was rubbed up into a fine paste, and the juices obtained by 
compressing it in a clean, sterilized cloth. This bloody juice was kept 
for twelve hours at a temperature of 10° C., and then sterilized by 
passing it through a Pasteur filter. Some of this juice was injected 
into a rabbit, which with twenty-five others was then made to re- 
spire an atmosphere charged with a spray of a bouillon culture of 
the micrococcus. As a result of this all of the rabbits died except the 
one which had previously been injected with the immunizing juice. 
In a similar experiment upon mice six of these animals, which had 
previously been injected with the immunizing juice, survived the in- 
jection of a full dose of a virulent culture, while a control mouse, 
not previously injected with the juice, promptly died after receiving 
the same quantity of the virulent culture. 
The writer in 1881, in experiments made to determine the value 
of various disinfectants, as tested upon this micrococcus, obtained 
experimental evidence that its virulence is attenuated by the action 
of certain antiseptic agents. Commenting upon the results of these 
experiments in my chapter on ‘‘ Attenuation of Virus,” in ‘‘ Bacte- 
ria” (1884), I say: 
‘‘Sodium hyposulphite and alcohol were the chemical reagents which 
produced the result noted in these experiments ; but it seems probable that 
a variety of antiseptic substances will be found to be equally effective when 
used in the proper proportion. Subsequent experiments have shown that 
neither of these agents is capable of destroying the vitality of this septic 
micrococcus in the proportion used (one per cent of sodium hyposulphite or 
