11 
sum:niary. 
The substance known as Danyz’s Virus consists of a culture of a bacil- 
lus belonging to the para colon group. It appears to be indeutical with 
the bacillus typhi murium of Loeffler. 
This organism is naturally pathogenic for mice, in which rodents it 
sometimes produces spontaneous epizootics. Its virulence has been 
raised and specialized by artificial means in the laboratory, so that it 
has become fatal for rats by ingestion. This artificial virulence is not 
very stable. It may be maintained under special conditions a few 
months, but the virulence is apt to fall off, especially on exposure to 
light and air. 
As far as rats are concerned, the effect depends somewhat on the 
amount ingested. Large amounts are frankly fatal. Small quantities 
are uncertain. Eats that survive the ingestion of the virus are ren- 
dered immune. Such rats may eat large amounts of the virulent virus 
with impunity. 
The infection caused in rats by eating the virus has feeble power of 
propagating itself from rat to rat. It, therefore, can not produce a wide- 
spread epizootic among these rodents. In practical use it must be 
spread around so that as many of the rats as possible will eat it. 
In many respects it resembles a chemical poison, with this great 
advantage, viz, that it is harmless, in so far as known, to man and 
domestic animals. It has the great disadvantage, that chemical poisons 
do not possess, of rendering the animals immune by the ingestion of 
amounts that are insufficient to kill, or by the ingestion of cultures that 
have lost a little of their virulence. 
In my experiments I succeeded in killing less than half the number 
(46 out of 115) of rats fed. The conditions in a cage are so much more 
favorable for the fatal action of the virus than could possibly be the 
case in nature that it is safe to assert that a less number would succumb 
in a wild state. 
The virus may, therefore, be used as one of the means in the fight 
against rats, bat it is far from being a sure means of exterminating 
these ro<lents in a particular place. 
