4 ESSENTIALS OF VETERINARY LAW 
one taken under police power may be destroyed, 
without any obligation on the part of any one 
to pay for it. Two veterinarians treating the ani- 
mals on adjoining farms in the same way may both 
lose their patients. One might be held legally 
liable for the value of the animal lost, and the 
other not liable, depending upon the underlying 
principle of his legal obligation. 
2. Common Law; Constitutions; Statutes. Many 
people imagine that if they know the statutes 
which have been enacted upon a certain point, they 
know all of the law necessary relative thereto. 
The fact is that there is a great body of the law 
which is not written in any statute, and it is this 
‘‘Common law’’ which gives to English speaking 
nations a peculiar system. It is evident that it 
would be a practical impossibility to cover all pos- 
sible points with enactments, and in fact it would 
frequently be undesirable so to do. Through the 
decisions of the English and American courts 
there have gradually been evolved certain princi- 
ples of law which find their use to a greater or less 
degree in almost all legal decisions. This body of 
principles is known as the common law. 
There are certain principles which have been 
adopted by the nation, and others by the separate 
states, and which have been put in definite form 
in words, and these documents are known as con- 
stitutions. They are so arranged that they are not 
easily changed. They are the charters under 
which the national and state governments work. 
No city ordinance, no executive order, no state 
statute is really law and binding, if it violate the 
principles of the constitution of its state, or of the 
