POLICE POWER 23 
that a man fully equipped according to modern 
standards would gain admission to practice where 
he chose. The medical profession is overcrowded, 
and the consequent difficulty in obtaining recip- 
rocal licenses has resulted in schemes for getting 
around the present condition by making all state 
boards recognize the authority of some national 
board. This condition may arise in the veterinary 
profession. According to past decisions such an 
arrangement is constitutionally impossible. 
13. Alienum Non Laedat. There is an old prin- 
ciple of the common law which is very powerful, 
even at the present time in spite of its age, which 
is known legally as alienum tuum non laedat; this 
means that a person may so enjoy the use of his 
own property that it shall work no injury to an- 
other. This is one of the principles of the police 
power which plays an important part in laws, 
ordinances, and executive action, as well as in 
court trials. A man may own a lot in town upon 
which he seeks to build a livery stable, or to erect 
a veterinary hospital. He may have actually 
spent a large amount of money in erecting the 
building and putting in the equipment. There 
may be no statute or ordinance prohibiting such 
use of the building, and he may have had the ap- 
proval of his plans by the city building inspectors. 
All these things may be true, and still before he 
attempts to use his building for the purpose in- 
tended he may be checked by an injunction. The 
Massachusetts court held that it is not necessary 
for the board of health to wait until a nuisance 
has actually occurred before getting an injunction 
