Oh, so that's what they said it was.
When I was a comic-reading kid - years after this ghastly ad, thanks - jujitsu was confined to tiny ads in the classified section. No one knew what it was, except it was like Karate, which was cooler because it was KARATE.
For some reason we thought it had to do with using your hand to poke people in the sternum.
Difficult to imagine a comic book today advertising a book that promised to tell kids “how to hit where it hurts,” let alone “how to apply the teeth-rattler,” but those days were different. In those days you could use the phrase "hard-hitting heroes" and actually name the bad guys, and recommend that bullies be discouraged with the application of more sophisticated force, and no one would lose bladder control and wonder what sort of monsters we were making our boys become.
Maybe no one cared because everyone knew the score: thousands would send away for the book. Number who learned ju-jistu: Zero.