Every year, an insidious epidemic strikes this place. It afflicts the human brain. Men who are ordinarily prudent, rational and businesslike find their vision clouded, their judgment impaired, their objectivity destroyed.

Owners and trainers of 3-year-old thoroughbreds will perceive virtues in their horses' performances and find excuses for their failures that are invisible to everyone else. They will be impervious to any evidence that might suggest that theirs is not a legitimate Kentucky Derby horse.

Take Tony Basile, for example. The successful veteran horseman ran his colt Television Studio in the Stepping Stone Purse here on Saturday, looking for some justification to put him in the Derby. He didn't get it. Television Studio finished third in the four-horse field, and did that only because the fourth horse went lame during the race.

"Not too bad," Basile said afterward. "He's in near-perfect condition for the Derby."

All week long, we hear the litany of rationalizations and excuses. Every horse in the Derby would have won every race of his career if he hadn't been blocked or bumped, carried wide, afflicted by a virus or hit in the eye by flying dirt clods. As a rule, handicappers ought to equip themselves with blinkers and earplugs and judge horses strictly off the cold dope.

But this week, one particular excuse is central to any analysis of the Derby. Every handicapper must decide whether Cure the Blues' eight-length defeat in his last start was a true bill, or whether it can be forgiven.

Four weeks ago, after he had run in the Gotham Stakes, Cure the Blues looked like one of the greatest racehorses alive. His performance in that one-mile event, said trainer LeRoy Jolley, "was one of the best races I've ever had a horse run -- anytime, anyplace."

Two weeks later, Cure the Blues virtually fell apart in the stretch run of the Wood Memorial Stakes, looking like a gutless, short-winded mediocrity who couldn't possibly have any Derby pretensions.

The ordinary trainer would have started formulating alibis before his horse had staggered to the finish line, but Jolley is one of the most cerebral members of his profession. He didn't win two Derbies and finish second on two other occasions in the last six years by engaging in self-deception. He watched the films of the Wood many times, scrutinized his horse and finally rejected the simplistic explanation that Cure the Blues fell apart because he can't run as far as a mile and one eighth.

"We'll never find an absolute explanation; there are no absolutes in this game," Jolley said. "In my opinion, it was one of those days when everything that could go wrong did go wrong. There were four or five situations that contributed to the defeat."

Jolley pointed out that Cure the Blues was coming into the Wood after an extraordinarily tough battle in the Gotham, one that could have taken a physical toll that he didn't realize at the time. He hooked up with Noble Nashua in a destructive speed duel over a racetrack that was deep, tiring and speed-retarding. When he sped into the first turn, Cure the Blues kicked himself and suffered a painful cut on his left hind leg. "It's a common occurence," Jolley said, "but a cut in the bony area is very painful when it occurs."

John Campo, the trainer of Wood winner Pleasant Colony, disputes this part of Jolley's analysis, and doubts that the cut would have affected Cure the Blues' performance. "The horse wouldn't feel nothing until the race was over," Campo said. "It wouldn't stop him from running. He looked to me like he just can't run around two turns."

Maybe. But Cure the Blues' performance in the Gotham was so brilliant, so gutty that it seems implausible that one extra furlong would make him look like a bum. His race in the Wood was almost too bad to be believed.

And with Jolley training him, he seems very likely to run at least a respectable race Saturday. Jolley is a master at getting his horses to run their best on the first Saturday in May. Genuine Risk finished third in the Wood and exploded to win the Derby; General Assembly ran dismally in the Wood and finished second in the 1979 Derby.

Cure the Blues may not be able to win Saturday, but he seems likely to give a performance that will demonstrate that the Wood was an aberration. This may be one of those rare instances in the Derby where a handicapper should perhaps ignore the cold evidence and give some credence to a trainer's interpretation of events.