16 
D. E. SALMON. 
in connection with infected pens at our experiment station in 
Washington. We have endeavored to be more precise than this, 
however, and have infected soil in various situations with the bac¬ 
teria of this disease, and then inoculated rabbits from this soil at 
regular periods. In this way the gradual loss of virulence in the 
microbe can be easily determined. At first the rabbits die in from 
six to eight days after inoculation, but this period grows longer 
and longer until finally the rabbits live twenty days and then the 
germ is no longer able to kill them. In our experiments we have 
found that this microbe loses all pathogenic properties after it has 
been in the soil but a few days longer than two months. 
The indication is, therefore, that the hog cholera germ is not one 
which preserves its existence indefinitely in the soil, or which can 
justly be considered an extra-organismal parasite. That it can 
multiply and live for a limited period in water and soil we have 
demonstrated, but in each case it soon loses its virulence and dies. 
How then is this microbe preserved from season to season, as 
it plainly is in certain cases, even when the disease has apparently 
died out in the meantime. Prof. Brown of England has frequent¬ 
ly expressed the opinion, with which we coincide, that chronic 
ulcerations of the intestine may exist in unsuspected animals and 
that these harbor and disseminate the microbe for an indefinite 
period. We find here, consequently, a condition somewhat analo¬ 
gous to what we find in contagious pleuro-pneumonia. The germ 
multiplies in the chronic lesion, for a time it appears to have but 
little virulence, and then suddenly and for reasons whieh are not 
well understood it is distributed as a most fatal contagion. Even 
the original host, which has carried it around with impunity for 
months, may suffer a fresh invasion and die from a hemorrhagic 
type of the disease. 
If there are other means by which this germ is preserved dur¬ 
ing the considerable periods of time which elapse between out¬ 
breaks of this malady we have not yet succeeded in demonstra¬ 
ting them. 
Hog cholera is, therefore, a strictly contagious disease. The 
virus as a rule appears to gain entrance to the body by way of the 
alimentary canal, and by means of soiled and infected food and 
water. It is possible that the respiratory passages also serve to 
