1. J Tannenbaum .Veterinary ethics: animal welfare, client relations, competition, and collegiality. 2nd ed. St Louis, Mo: CV Mosby Co, 1995 ;154 ,166 -170 , 166 .
2. T Regan .The case for animal rights. Berkeley, Calif: University of California Press, 1983 ;236 -248 , 236 -248 , 236 .