FORT WORTH, Texas — Authorities raided a well-known veterinary clinic Tuesday morning, seizing two dogs, after a woman said a dog she took in to be euthanized was being kept alive and used for blood transfusions.

Fort Worth police and officers from the Texas Board of Veterinary Medical Examiners were inside the Camp Bowie Animal Clinic in west Fort Worth.

Lou Tierce, a longtime Fort Worth veterinarian, is accused of deceiving Jamie and Marian Harris, of Aledo, Texas, into believing that their 5-year-old Leonberger named Sid was euthanized last fall because of a degenerative spinal condition.

In fact, Sid was being “bled” for plasma and other experimental treatments, Marian Harris said.

The family filed a complaint with the state last week.

Jim Eggleston, a Weatherford, Texas, attorney who is representing the Harris family, said allegations have surfaced that more dogs and cats — some with serious illnesses — were being kept alive for blood transfusions and other experimental treatments.

Sgt. Raymond Bush, a police spokesman, said police received a criminal complaint last week that animals were being mistreated — and stolen from clients — at the clinic.

“If the city of Fort Worth is able to determine that the law was broken, then down the road, warrants could be issued for somebody’s arrest,” Bush said.

The raid began shortly before 10 a.m., when animal-control officers and plain-clothed investigators parked at a vacant fried-chicken restaurant next to the clinic. Two of the investigators went inside while the others talked to a female employee who was loading supplies into her car.

By afternoon, animal-control workers carried out two dogs, one in a carrier, from the clinic.

“At this point, these animals are evidence,” Bush said.

Marian Harris said she was “shocked” when she got a call on April 21 from a former veterinary technician at the clinic, telling her that Sid was still alive. The employee told Harris that she quit that day because she could no longer work in a clinic where the animals were mistreated.

Jamie and Marian Harris described how they drove to the clinic and while two friends guarded the front and back doors as her husband distracted the receptionist, Harris went to the back, found Sid in a cage and rescued him from the clinic.

Tierce had told the Harrises that he wanted to use a new “cold laser” procedure and that it might take longer for the dog to recover.

In September, Jamie Harris went to Tierce’s clinic to see Sid and was shocked when the dog dragged himself into the lobby on his hind quarters. Harris was told that Sid was suffering from side effects from a medication cocktail and that Sid had a congenital spinal defect and would have to be put down.