The device: One seven-week race meet at Del Mar, California. The date: July, 1975. The author: A New York writer whose love affair with the track has handicapped him up and down the economic ladder since he was about sixteen. This, he claims, is his equine swan-song, a saturation effort that should purge his soul forever of the vagaries of the races. His readers get the benefit of his experience in this chronicle of What Makes Telly's Pop Run, as we're told about the trainers, the jockeys, the owners, the handicappers, the exercise boys, and finally, the horses, whose idiosyncracies make or break all the two-legged mammals at the track. For someone who knows the business, this is fun. For the neophyte, it's a horse of another color . . . an education.