118 
The Rot in Sheep. 
hcpatica of the sheep and other mammalia has not as yet been fully 
ascertained, we see no reason to doubt that they follow the law 
of development belonjjing to flukes in general. Until, therefore, 
direct experiments shall have shown to the contrary, we shall 
continue to hold the opinion that the several metamorphoses of 
all the distomata are regulated by the same laws. Sheep, we 
believe in common with mammalian animals in general, receive 
the cercarice in their -puixi state, and not as free living forms. If 
the contrary were the case, it is evident that the cercarioB would 
have to undergo their pupa change within the digestive organs, 
and, judging from analogy, they would have as free cercarice to 
first imbed themselves in the mucous membrane for this purpose. 
We do not regard this as being at all probable ; besides which, 
we have seen that in De la Valette's experiment of administering 
free cercaria; to Avarm-blooded animals, he failed in producing 
distomata, and only succeeded when he gave them in their jmpa 
condition. 
Although distomata are so widely diffused, it is an established 
fact that ruminating animals are more frequently affected with 
them than others, and sheep most of all. We have directed atten- 
tion to the latter-named circumstance in treating of the causes of 
rot, and have there said that the probable explanation of it was 
that the natural habits of the sheep led to its cropping the short 
grasses and feeding near to the ground, where the penultimate 
forms of distomata abound. The greater susceptibility, however, 
of ruminating animals would seem to depend on other causes, 
and to be rightly accounted for by reference to the special functions 
of their digestive organs. Encysted cercaria; received with the 
food of ruminants are not at once exposed to the solvent action 
of the gastric juice, but are detained for an indefinite length of 
time within the rumen and the other preparatory stomachs whose 
secretion is non-digestive. Within these organs, therefore, no 
special cause of destruction to the vitality of the cercaria: exists, 
and hence a greater number of distomata are perfected, ulti- 
mately to find their way into the bile-ducts by passing firstly into 
the true digestive stomach and onwards into the duodenum. The 
converse is the case with regard to the simple-stomached herbi- 
vora and other mammals, viz., that the encysted cercarice, on enter- 
ing the digestive system, are immediately exposed to the action 
of the gastric juice, by which many of them are doubtless destroyed, 
and consequently do not reach their proper habitat — the liver. 
This circumstance may account in part for the well-known 
fact that horses graze almost with impunity on pastures where 
both oxen and sheep become affected with flukes. Other causes, 
without doubt, influence this immunity ; among which must be 
placed the general plan adopted in rearing horses, which, together 
