6 
The bouillon used was made from horse meat with 1 per cent peptone, 
and to which was added a little carbonate of lime to neutralize the acids 
which are formed during culture and which rapidly diminish the viru- 
lence of the microbe. 
After this long and painstaking procedure, Danyz obtained a very 
virulent culture that, contained in flasks and kept from the influence of 
light and air, preserved its virulence for several months. Planted on 
agar it preserved its virulence without appreciable diminution for two 
months. In bouillon, in flasks or tubes stoppered with cotton, it altered 
very rapidly. 
One can not read the foregoing account without admiration for the 
patience and perseverance required to increase the virulence of an 
organism by so many passages through the peritoneal cavities of rats by 
means of the collodion sack method. 
DESCRIPTION OF THE ORGANISM. 
The cultures with which I did the following work were obtained from 
the Pasteur Institute. 
The organism is a cocco-bacillus, showing distinct motility. Stains 
well by the ordinary stains and does not stain by Gram’s method. 
It grows well at ordinary room temperature ; also in the incubator, 
and on all the ordinary media. In bouillon it produces a uniform 
cloudiness in twenty-four hours. A slight scum forms after several 
days’ growth, which falls to the bottom when shaken. In Dunham’s 
solution it grows well, but produces no indol in twenty-four hours’ 
growth. 
It turns blue litmus milk red, but does not cause coagulation. 
It grows the whole length of the stab in gelatin, forming small whitish 
colonies in the deeper portions of the tube. It does not grow over the 
entire surface of the gelatin tubes. Does not liquify. 
It grows uoder anaerobic conditions. 
It ferments glucose bouillon, but not lactose bouillon. 
In glucose bouillon it produces I-CO 2 , 5-H. 
It also produces H 2 S. 
From a general biological standpoint it is plain that this bacillus 
belongs to the para colon group, and is very similar to the bacillus of 
rabbit septicaemia, hog cholera, and icteroides — as far as its morpholog- 
ical and cultural characteristics are concerned. 
VIRULENCE OF THE VIRUS FOR RATS. 
One hundred and flfteen rats were fed with the cultures in various 
ways during the course of my experiments with the virus. Of these, 
46 died — less than half. 
Most of the rats used were the gray rat (m. decumanus) and the tame 
white rat. A few (8) of the wild brown, or Norway rat, were used. 
