86 ESSENTIALS OF VETERINARY LAW 
or may not, have authority to order the killing. 
If he has the authority the veterinarian acting 
under such orders would be protected; but if he 
does not have the authority the veterinarian acts 
at his own peril. The veterinarian may know that 
the killing is justifiable, but he must be prepared 
to make proof of the fact which will convince the 
court in the face of conflicting testimony. It is 
ordinarily considered that a horse with a broken 
leg is useless and without value, but this is not 
always true. The writer once had a valuable colt 
whose hock was broken squarely across. Never- 
theless complete union occurred, and the horse did 
many years of hard service, and was locally known 
as a fast, long distance roadster, and he never 
showed lameness. A mare, though lame from the 
fracture of a small bone, was still of value for 
breeding. In either case, had a veterinarian taken 
the responsibility of killing the animal, he would 
have assumed a liability for its loss. 
57. Burden of Proof. It is a general rule of 
law that the one making a claim must prove it. 
The fact that a man is practicing veterinary medi- 
cine would be generally taken as an evidence of 
his competency in that profession, aside from the 
question of his right to practice. In his care of 
the case the law presumes that he has used due 
care and diligence, in accord with the state of the 
science. He is not generally called upon to prove 
that he is competent, but it becomes the duty of 
one claiming to have been injured through his 
malpractice or negligence to prove the fact to the 
jury. When he has introduced evidence to show 
negligence or malpractice the defendant has an 
