I feel requiring written consent would cause a lot of unnessesary work for veterinary practices that would make them less likely to take on externs.  I can certainly appreciate the publics concern for their pets but after reading other comments there is a huge misconception about what goes on in the back of a vet clinic. As it stands externs are well supervised and are not going to be doing anything to put someones pet in danger.  A veternarian or licensed technician is not going to have a student practicing on a critically ill patient or a patient with horrible veins.  If anything people should be more concerned about the completely untrained people who by our current laws are allowed to draw blood, take x-rays, give medications to their animals.  Will you make veterinarians have owners sign written consent that Joe Shmo off the street with out any education will be pulling Fluffys blood today?