642 DISEASE IN WILD MAMMALS AND BIRDS 
and hardness; and fine yellow lines could sometimes be 
made out twisting over the surface. 
The disease affects wild rats differently from prairie 
dogs. In both the spontaneous and experimental disease 
the infestment was insignificant, amounting to perhaps 
three or four foci the size of a split pea near the anterior 
margins of the liver. Diagnosis may be easily confirmed 
by crushing the yellow infested portions of the liver 
between glass slides and examining microscopically 
for ova. 
We have seen such a small number of cases of this 
disease because so few prairie dogs reach the autopsy 
table, yet there must be some important mortal factor 
in our prairie dog enclosure, for the Superintendent 
states that the population there does not increase in spite 
of the frequent births and additions from dealers. The 
animals almost invariably die under ground and their 
bodies are not recovered. 
In order to test out the origin of the infestment we 
trapped two of our exliibition specimens, and the liver of 
both was found infested on surgical examination whereas 
six newly purchased ones had normal livers. The latter 
were secured fresh from their native habitat in the West, 
and their livers were examined through long surgical 
incisions and found free of infestment. Later we fed the 
ova (embryophores) from rat livers to these prairie dogs 
and on destroying them found them infested. We were 
also successful in transmitting the disease in the oppo- 
site direction, i.e., from prairie dog liver to white 
rat. From all this we feel sure that the prairie dog 
disease in our Garden was transmitted from the rat and 
that here is another reason for rat extermination in a 
zoological garden. 
The adult Hepaticola hepatica of prairie dogs I have 
not seen in sufl&cient entirety to compare with the rat spe- 
cies and therefore cannot affirm that the two are identical 
species. It is presumably like that of the rat, being thread- 
