Macmillan, 1903, approximately 32,000 words. Available for free on Project Gutenberg.
Buck, a sturdy crossbreed canine (half St. Bernard, half Shepard), is a dog born to luxury and raised in a sheltered Californian home. But then he is kidnapped and sold to be a sled dog in the harsh and frozen Yukon Territory. Passed from master to master, Buck embarks on an extraordinary journey, proving his unbreakable spirit...
First published in 1903, The Call of the Wild is regarded as Jack London's masterpiece. Based on London's experiences as a gold prospector in the Canadian wilderness and his ideas about nature and the struggle for existence, The Call of the Wild is a tale about unbreakable spirit and the fight for survival in the frozen Alaskan Klondike.
It's really a barbarian epic starring a dog.
My complete list of book reviews.