If you are a dog lover, then this is a difficult story to read.  The story is narrated by a dog that saves its human family's baby from a fire.  The dog receives praise and adoration for the rescue.  Unfortunately, the owner performs an experiment on the dog's puppy, and the experiment kills the puppy.  The narrating dog remains by the puppy's grave for weeks.  By the end of the story, the dog is dying from starvation. 

The story says a lot about human nature by contrasting the dog with the master.  Readers are told that the dog has been told from a very young age that its purpose in life is to be selfless.  The dog is supposed to live for others and make sure that the needs of people around it are met before its own needs.  

. . . we were sent into this world for a wise and good purpose, and must do our duties without repining, take our life as we might find it, live it for the best good of others, and never mind about the results; they were not our affair. She said men who did like this would have a noble and beautiful reward by and by in another world, and although we animals would not go there, to do well and right without reward would give to our brief lives a worthiness and dignity which in itself would be a reward. 

That's exactly how the narrating dog lives.  She puts her own life in danger in order to rescue the baby from the fire.  She successfully rescues the child; however, she is beaten because the master doesn't understand what the dog was doing with the baby.  The narrator is prepared to leave the house forever, but can't bring herself to leave her puppy.  

Why, what would life be without my puppy!

That was despair. There was no plan for me; I saw that; I must stay where I was; stay, and wait, and take what might come—it was not my affair; that was what life is—my mother had said it.

Eventually, the master learns the truth about what the dog had done, and he is full of wonderful praise for the dog.  

They disputed and disputed, and I was the very center of subject of it all, and I wished my mother could know that this grand honor had come to me; it would have made her proud.

Unfortunately, this is the point in the story where readers learn that while dogs are selfless creatures, human beings are selfish. The master is a scientist, and he cares about his experiments and his reputation more than he cares for the life of a non-human.  In order to prove his hypothesis about eyesight, the master performs a brutal and bloody experiment on the puppy.

They discussed and experimented, and then suddenly the puppy shrieked, and they set him on the floor, and he went staggering around, with his head all bloody, and the master clapped his hands and shouted:

“There, I’ve won—confess it! He’s as blind as a bat!”

The puppy dies from the trauma inflicted upon it, but the owner doesn't care.  He's getting the praise that he loves.  

“It’s so—you’ve proved your theory, and suffering humanity owes you a great debt from henceforth,” and they crowded around him, and wrung his hand cordially and thankfully, and praised him.

He coldly tells his servant to bury the puppy.  He doesn't care about the puppy's death, and he doesn't care that the puppy is the puppy of the dog that saved his own child's life.  The dog gave life to the man's child, but the man took life from the dog's offspring.  Readers can assume that the other affluent men and women in the story have an equally cold and selfish human nature because it's only the servants that recognize the cruelty of the master. 

When the footman had finished and covered little Robin up, he patted my head, and there were tears in his eyes, and he said: “Poor little doggie, you saved HIS child!”

Mark Twain's "A Dog's Tale," is the story of a dog who saves a family's child from a fire in the nursery. The dog has a puppy of her own, and the master, a scientist, does scientific tests on the puppy, which ultimately kills it. The footman buries the puppy: "When the footman had finished and covered little Robin up, he patted my head, and there were tears in his eyes, and he said: 'Poor little doggie, you saved HIS child!' " The dog had saved the child of the master, but the master kills the dog's child. This reveals that some humans only act in their own interest, and even if one does something nice for a person, the person may never repay that kindness. The master in the story treated the dog as though the dog had no feelings and didn't matter, even though the dog risked his life for the master's baby.