PART Vv. 
THE DOG AND HIS DISEASES. 
INTRODUCTION. 
f 
ORIGIN AND TRAITS. 
N the origin of the dog scientific men have differed 
widely. By some he has been declared a de- 
scendant of the wolf, and by others of the fox 
or jackal, and points of resemblance, such as 
cranial development, period of gestation, peculiarity 
of the eyes or carriage of the tail, have been cited 
in support of each theory. Still other writers 
have claimed he is of a distinct breed, and have 
attempted to prove this by the assertion that, though 
he will breed with all of the above animals, the progeny of the cross 
are incapable of propagation zzzer se, thus proving they are true hybrids, 
or descendants of distinct species, it being a well-established principle that 
hybrids are sterile if bred together. This theory has, “however, been 
completely refuted by observation of the dogs of the Indian tribes, as 
it has been proved beyond question that these cohabit with the wolves, 
foxes and coyotes, and that the progeny of these unions are as fertile 
as any others. From this fact modern authorities have come to the 
conclusion that the dog is a mongrel, descended from crosses between all 
the animals to which he bears resemblance, and raised to his present per- 
fection by selection and breeding for specific results. Animals in a state 
of nature vary but little if any from the original types, because they are 
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