Before Dr. Ivan Pavlov won worldwide fame for his experiment proving that dogs could be made to salivate at the ringing of a bell, he performed a nearly identical experiment on his younger brother, Nikolai. That experiment and its regrettable aftermath have only recently come to light, but they have already added fuel to the ongoing ethical debate over whether it is better to conduct scientific experiments on laboratory animals or on one’s own relatives.

In the spring of 1903, Pavlov attended a Sunday brunch in St. Petersburg with his parents and Nikolai, an unemployed hat designer whose envy of his celebrated brother bordered on loathing. As Pavlov talked about his plans to study the salivary reflexes of dogs, his brother could be heard muttering the words “douche bag” into his borscht. Pavlov was midsentence when his mother suddenly interrupted him.

“Why are you using a dog and not your brother?” she asked. “He can drool with the best of them.”

“Mother, I know what I’m doing,” Pavlov said.

“What you’re doing is giving away a job that should be your brother’s to some dog you don’t even know.”

Pavlov looked beseechingly at his father, but the old man, worn down by decades of living with Mrs. Pavlov, offered only a familiar look of resignation. “It will be a nice way for you boys to spend some time together,” he said.

From the moment the Pavlov brothers entered the laboratory, their enmity was palpable. Nikolai resented being treated like the subject of a science experiment; Pavlov resented the fact that Nikolai was not a dog. Choosing a dish that would make Nikolai’s mouth water became the first of many battlegrounds. Nikolai demanded that his brother feed him beluga caviar, arguing that this was the only food that made him drool on a consistent basis. Pavlov hit the roof, angrily informing his brother that scientists, particularly those in the field of saliva research, were not made of money. After much bickering, caviar was out and croutons were in.

On the first two days of the experiment, Pavlov repeatedly presented croutons to Nikolai, rang a bell, and waited for his brother to drool on cue. Pavlov wrote in his journal, “My brother is an incredible pain in the ass, but his salivary reflexes are superb.” On the third day, however, the experiment took a sudden turn. When Pavlov rang the bell but refused to produce any croutons, Nikolai responded with a roundhouse punch to his brother’s nose, putting him in the hospital. His mother visited the injured scientist but showed little sympathy. “What were you thinking, ringing the bell but not feeding him anything?” she asked. “You know how cranky Nikolai gets when he’s hungry.”

With Pavlov out of action, Nikolai trolled St. Petersburg’s cafés and night spots, telling anyone who would listen how well “his” amazing experiment was going. Nikolai’s self-promotion reached its apex in a glowing profile in the Sunday Styles section of the St. Petersburg Times, in which Nikolai dismissed Pavlov’s role in the laboratory. “He just writes things down,” Nikolai was quoted as saying. “I’m the one who’s doing all of the drooling.” Reading this libel in his hospital bed, his broken nose still in a splint, Pavlov decided that he had finally had enough.

The next day, Pavlov replaced his brother with a female collie. The two never spoke again, unless one counts an obscene telegram from the autumn of 1903, which most scholars attribute to Nikolai. In his Nobel speech, Pavlov thanked God, his agent, and the collie, but made no mention of his brother. Nikolai faded into obscurity, eventually becoming an assistant bookkeeper at a St. Petersburg eraser factory. Those who remembered him from this last, sad phase of his life said that he never gave the slightest hint of having played such a pivotal role in the history of science, except when the telephone rang.