I bought this book second hand after reading about it in the back of Cats Cradle and was quite intrigued, but in the end disappointed. I am really only writing about it to keep a record of everything I have read, and I wouldn't dismiss it so completely as to forget I read it.
The premise is so interesting, the idea of an animal with a human consciousness, but the more I read the less convinced I was. So this scientist is trying to create super-sub-human intelligent creature. For a start there is a lot of very objectionable vivisection going on here, merely to satisfy one man's curiosity. Eventually he achieves the desired result of a dog with a human sized brain, who is brought up alongside his own daughter, Plaxy. Why he should have arrested physical development was not adequately explained, because he grows up at the same rate as the human baby, with whom he develops a very close bond. The story is related by the future husband of Plaxy, who seeks out the mysterious girlfriend who has deserted him, and finds a very strange family history and even stranger friendship with the dog Sirius.
The book is supposed to be about the nature of animals and the nature of human beings, and what makes the difference. But in the end I found the whole story to be just mistaken. Why would having a bigger brain cause him to learn speech ... not logical since he has not the capacity to form words. Why would it make him think like a human. It makes all the wrong assumptions about the nature of intelligence. Then why would Trelone, the scientist, treat him like a human being, an individual, like a member of the family, and then send him off to train to be a sheepdog as soon as he was mature. The experiment has the logical outcome that of course the creature is not sure if he is a dog or something more, which means he is fighting a constant battle between his wild, animal nature and his intelligence. In the end Sirius is not a very good dog and not a very good human being. And you have the fairly predictable tragic ending, with ordinary people being afraid of something they do not understand. A story of science gone mad, saying far more about humans than about dogs, and very little about intelligence. The book predates wide knowledge about DNA and so Trelone uses hormones to manipulate the subjects of his experiments, but I think the lesson is the same ... beware of playing god.