Dear Dr. John: I have two cats. Pierre is about 3 years old and white. Patrick is about 8 years old and is black. Last May Pierre had his first feline leukemia vaccine and I took him back for the second with no trouble at all. Patrick had never had feline leukemia shots but had been vaccinated for rabies and distemper with no problem. His first leukemia shot knocked him right off his feet because at home he would not eat. The next week I took him back and told the vet how it affected him. She said she did not dare to give him the second one. The vet explained this ailment to me but I still don’t know what she meant. — M.N.L.

Dear M.N.L.: Based on the papers you sent and your description of the sequence of events, it seems as if your cat tested negative for feline leukemia virus and was being vaccinated to prevent him from contracting the disease. The first vaccine was given and caused a bad reaction. Because of what you described to the veterinarian, she felt that the booster leukemia vaccine might cause further illness and perhaps an immediate anaphylactic or allergic reaction which could even cause death. Your cat does not have feline leukemia now. Your veterinarian is simply trying to avoid any possible unnecessary complications.

Dear Dr. John: I am interested in finding out something about our 9-month-old dog of mixed breed. He has a star on his forehead. He is playful and thinks he is smart when he makes us laugh. He has a black tongue like a Chow but is much bigger and has no long hair. Enclosed is a picture. — M.W.

Dear M.W.: Based on your photograph, all I can say is that you own a mixed breed Chow or Akita. They have black tongues and it is seen in dogs possessing such breed in their bloodline.

Dr. John de Jong is a Boston-area veterinarian and self-syndicated columnist.