The image of Lou Gehrig saying farewell to Yankees fans, his head bowed as he speaks into a cluster of microphones near home plate on July 4, 1939, remains indelible, even after 75 years.

Gehrig's 274-word speech that day -- the words of a man who likely knew he was dying from a horrifying degenerative disease -- expressed optimism and gratitude. It endures as the most iconic speech in sports history.

On Friday, the 75th anniversary of Gehrig's address, Major League Baseball will commemorate the moment by presenting a video of each current team's first baseman reciting a line from the speech. The Yankees will show the tribute first on Wednesday.

More than words

Gehrig, known as the Iron Horse, began a streak of 2,130 consecutive games on June 1, 1925, in Chicago. Weakened and no longer possessing his skills, he stepped aside for Babe Dahlgren on May 2, 1939, in Detroit.

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Amyotrophic lateral sclerosis (ALS) is the official name for Lou Gehrig's disease, a deterioration of nerve cells in the brain and spinal cord. It robbed him of his strength and motor skills and eventually his life. Gehrig's forced departure at age 36 strikes a chord with all who have played the game.

"I'm fortunate to be in a situation where I've decided this is going to be my last year,'' Derek Jeter said. "With Gehrig, it goes beyond what any other player experienced because of his health.''

Jeter has watched Gehrig's speech many times. "I can't imagine what that would be like,'' he said. "I don't know how he kept it together. It takes a lot of courage. All of us can only do this particular job that we do for so many years. I don't care who you are, how good you are. But afterward, life goes on -- you hope. So it's not like your life is over with, your career's over with. Unfortunately for him, his life ended way too soon.''

Gehrig's words that day helped sustain the family of Jim "Catfish'' Hunter in 1998 when the Hall of Fame pitcher was diagnosed with ALS. "Gehrig looked at it like he was going to live his life to the fullest, all the days that he was given, even if he had this terrible disease,'' said Helen Hunter, the pitcher's widow. "Jim was bound to live his life as long as he could.''

Hunter, who pitched for the A's and Yankees, died in 1999 at 53.

They had no idea

More than 61,000 fans were at Yankee Stadium that Tuesday for a holiday doubleheader with Washington on Lou Gehrig Appreciation Day. They knew it was the end of Gehrig's Hall of Fame-worthy career, but at the time, there was no clear indication about his medical condition.

About a month earlier, Gehrig had been diagnosed with ALS, but published reports likened the affliction to poliomyelitis, which had stricken President Franklin D. Roosevelt. The perception was that Gehrig was on the way to being disabled, not dying.

"My own impression was that he was very sick,'' said Ray Robinson, author of "Iron Horse: Lou Gehrig in His Time.'' Robinson, now 93, watched from the stands that day. "I had no idea he was destined to die very quickly. From the statement issued by the Mayo Clinic, it was impossible to ascertain that Gehrig was destined to die very quickly from some strange thing called ALS.''

Robinson described the scene that afternoon. "The fog created by the cigarette smoke descended on the field and sometimes you could hardly see what was going on at home plate. I would say the feeling was kind of mournful. I think they knew he probably wasn't going to play anymore. I doubt very much anyone outside of a very knowledgeable doctor knew he was dying. He delivered those words without any paper in front of him. I was deeply touched. I could imagine that people had tears in their eyes. They were there to say goodbye to a man they considered a decent, honest, resolute fellow.''

In the bleachers that day was Irving Welzer, who would become a Tony Award-winning producer. "We didn't know what was wrong with him,'' said Welzer, 86. "He wasn't hitting, wasn't fielding. We just thought it was the end of his career."

About a month earlier, Gehrig had been examined at the Mayo Clinic in Rochester, Minnesota, by Dr. Harold Habein, whose mother had suffered from ALS, according to the doctor's son.

"The doctors in New York didn't know what was the matter and Lou's wife [Eleanor] called the Mayo Clinic and talked to Dr. [Charles William] Mayo, who often had my father see patients," Harold Habein Jr. said. "My father said he saw the signs, the neurological deficits, the atrophy of his muscles.''

Habein put Gehrig in the care of Dr. Paul O'Leary. Habein Jr. said Gehrig's wife asked O'Leary not to tell her husband the severity of his illness. "But people who have it have a good mind,'' said Habein, a retired physician. "They can see they are deteriorating by the day.''

Jay Youmans, O'Leary's nephew, said his family does not know what private conversations O'Leary may have had with Gehrig about his illness.

"I don't know that he sat him down and said, 'Lou, this is what you are faced with.' ''

'I'm not playing anymore'

It is also uncertain what Yankees management or players knew about Gehrig's condition leading to his farewell speech. In 1938, Gehrig finished with 170 hits, 29 home runs and a .295 batting average. Not bad, but nothing near his lifetime averages of .340, with 202 hits and 37 home runs.

According to Dahlgren's son Ray, his father told him that Gehrig appeared to be displaying symptoms during spring training of 1939.

"They were taking infield, Gehrig was running back toward first base, [second baseman] Joe Gordon made a couple of throws and [Gehrig] stumbled and fell. My dad was right behind him. My dad said 'Are you OK.' Lou said, 'These old legs are not the same.' "

The Yankees opened the 1939 season on April 20 against Boston and Gehrig made an error and went 0-for-4. The next day, in Washington, he went 1-for-3 and made another error. On April 30, the last day of his consecutive-games streak, he went 0-for-4 against Washington.

On May 2 in Detroit, manager Joe McCarthy replaced him with Dahlgren. "My dad said when you walked into the clubhouse, you could hear a pin drop,'' Ray Dahlgren said.

As the game progressed, Ray Dahlgren said, his father told him he had implored Gehrig to replace him so he could maintain his streak. "My dad says in the third inning, 'Go out there.' Lou tells him, 'You're doing fine.' In the fifth, he says the same. Lou says, 'You're doing fine.' My dad says, 'Just walk out there, keep your streak going.' My dad says he says, 'Babe, it's over.' He said, 'What do you mean, it's over?' He said 'I'm not playing anymore.' He said when Gehrig told him that, it raised the hairs on the back of his neck.''

Gehrig never played again.

Hall of Famer Bobby Doerr, 96, is believed to be the only living former major-leaguer to have played in a game with Gehrig. In a comment through a spokesman, Doerr, who played second base for the Red Sox from 1937-51, called Gehrig "a great man and a great player.''

On the day of the speech, some of the Yankees were told that Gehrig was ailing and might need help during the on-field ceremony. "McCarthy told my dad and a couple of other guys to line up close to Gehrig, the reason being in case he fell," Ray Dalhgren said. "He wasn't stable at the time.''

Dahlgren also spoke of a conversation his father overheard between Babe Ruth and Gehrig, who had been feuding for several years. "Let's knock it off,'' Dahlgren overheard Ruth say as Gehrig wept.

Gehrig had not intended to speak. "He had a long prepared speech,'' said Stephen Sundra, whose father, Steve, pitched for the 1939 Yankees. "My mom related the story that my dad said Lou was so emotional that he couldn't go by the written speech.'' But urged on by McCarthy and general manager Ed Barrow, Gehrig delivered his immortal words.

The long goodbye

Gehrig remained with the Yankees for the rest of the 1939 season, even as his condition worsened and he had problems lifting his arms.

Dahlgren's son said his father told him: "Gehrig came up to my dad in the dugout and says, 'Hey, Babe, can you light a cigarette and put it in my mouth?' Here he is smoking a cigarette and my dad is pulling it in and out of his mouth. During the World Series, [Frank] Sinatra comes into the dugout and Dad wanted to cross his legs. He had one of the players help him cross his legs as he was sitting on the bench.''

Gehrig's last day in the Yankees clubhouse came after the World Series. There was no emotional scene, Dahlgren said his father told him, because there still was no definitive word on Gehrig's future. Gehrig gave his glove to a batboy, who determined he had no use for the lefthanded mitt and passed it on to Dahlgren, who later sold it to a collector, his son said.

Gehrig died June 2, 1941, in his home at 5204 Delafield Ave. in Riverdale, about 61/2 miles from Yankee Stadium. He was 37. It was a few weeks after a final visit from Dr. Habein.

"He said he saw Lou and it was obvious Lou was not going to live much longer,'' the doctor's son said. "He knew it was inevitable as he had watched his own mother die.''

Gehrig's speech would echo through the generations. Mickey Mantle embraced Gehrig's words during his retirement speech at the Stadium in 1969, saying, "I never knew how someone dying could say he was the luckiest man in the world. But now I understand."

Gehrig's impact on baseball never faded and came sharply into focus when Cal Ripken Jr. approached and then surpassed his consecutive-game streak in 1995, extending the record to 2,632 games. The striking difference between the two is that Ripken ended the streak of his own volition.

"When you are in the streak, you are not thinking about the ending. It's just a new day,'' the Hall of Fame infielder said. "I would assume he never wanted to come out. I think we all live with the fact that something could happen to us. In a baseball sense, I don't think that we think something else could happen that would take baseball away. That is sad to think about.''

Ripken said that when he surpassed Gehrig's mark, "The meaning was much greater than the number because of his legacy, who he is.''

In 2013, Alex Rodriguez broke Gehrig's record for grand slams by hitting his 24th. "Lou Gehrig is an icon and to even be mentioned with him is an honor,'' Rodriguez said in a recent e-mail. "He still represents greatness in baseball and as a human being.''

Gehrig had 493 career homers and a .340 lifetime batting average. He won the Triple Crown in 1934.

"His numbers get lost because of the disease,'' Yankees first baseman Mark Teixeira said. "But as for his speech, it's a great message to tell everybody no matter what your lot in life, be thankful for what you have. He was a wise man. His words ring true for everybody, not just athletes.''

Northeastern University law professor Roger Abrams, who has authored several books on baseball history, spoke about why Gehrig's speech still matters all these years later.

"He's taken on mythic proportions,'' he said. "Baseball really reflects American society, and in every myth, you need the tragic figure. And he, after just an extraordinary career, becomes the tragic figure of what had happened to America in the 1930s. A terrible decade of Depression. In some ways he suffered for us all. He was a representative of the American spirit even when faced with just extraordinary personal tragedy. He saw the glass as not just half full, it was overflowing. I think he was genuinely thankful for the opportunity he had.''