The National Zoo's giant panda cub is now nearly two feet long, weighs about 71/2 pounds and calmly submitted to his first vaccination yesterday. And, in a banner week of development, the baby panda has started to bark.

The 2-month-old cub, barely the size of a stick of butter at his birth July 9, has grown more than nine inches and gained more than five pounds since zoo veterinarians first examined him early last month. He is 211/4 inches long and has a tummy girth of a robust 15 inches.

Members of the zoo's animal care staff say the cub appears healthy and continues to get stronger and more confident every day. He can raise himself on his front legs and continues attempting to crawl. At one point Wednesday, according to a report from the Panda House, the cub "pulled himself onto his fore legs and barked, one loud sharp bark. We were amazed at the intensity of it. What a little bear!"

Yesterday's exam, his fifth, lasted 16 minutes and included a vaccination against the canine distemper virus. He will receive his remaining distemper and rabies vaccines during the next two months, zoo officials said.

"He was pretty placid during the whole exam," said zoo spokesman John Gibbons. "He didn't even react to the injection. You can see in the exam picture, he's not even looking back to see what's going on."

The cub, who was weighed, measured and had his heart rate checked, "was content to just lie on his belly and let the veterinarians do what they had to do," Gibbons said.

It is customary with mammals to wait until they are 8 to 10 weeks old to begin giving them their shots. The zoo's veterinarians said this is when antibodies in the mother's milk are believed to begin declining -- and a cub's immune system starts strengthening on its own.

Mother Mei Xiang did not seem to be alarmed by the cub's yelp. She spends more time away from her cub and has started going into the yard.

On Wednesday, her mate, Tian Tian, was in the next yard. He approached the wire mesh fence that separates the two yards and the pair "calmly and playfully interacted," the zoo reports.

The cub, conceived through artificial insemination, is the first of this endangered species to be born and survive at the zoo in its decades-long quest to help breed giant pandas. He is the first offspring of Mei Xiang and Tian Tian, who arrived at the Panda House in late 2000 on a 10-year loan from China.

The zoo is paying China $10 million in privately raised funds for the panda pair and $600,000 for the cub. The money is earmarked for conservation projects to save giant pandas in the wild.

Following Chinese custom, the cub won't get a name until he is 100 days old. Friends of the National Zoo, the animal park's support organization, is holding a contest on its Web site in which the public can vote for a favorite name among five approved by the China Wildlife Conservation Association.

Under the agreement with China, the cub is considered the property of that country and will be sent there after his second birthday.

For links to webcams of the panda and more information, go to

AGE: 31/2 weeks WEIGHT: 1.8 pounds

LENGTH: 12 inchesAGE: almost 6 weeks WEIGHT: 4.2 pounds

LENGTH: 17 inchesAGE: 2 months WEIGHT: 71/2 pounds LENGTH: 211/4 inches"He was pretty placid during the whole exam," a zoo official says of the cub. "He didn't even react to the injection."