From Gustav Mahler: Memories and Letters, by Alma Mahler, page 162: "New World, 1909 (in New York City)"

“On again. Rats with long pigtails slunk nimbly and rapidly along the walls of the stinking street. Mahler said: ‘I can hardly believe that these are my brothers.’

On again. Small shops, small hotels, but all silent. Finally, on the outskirts of this district we came on the habitat of a religious sect. There was a large hall at the far end of which sat a man with the face of a fanatic playing hymns on a harmonium in a pronouncedly whining style. The benches were occupied by a starving congregation. We were given the explanation. For listening to the hymns and joining in – a cup of coffee and a roll. What wretchedness in those faces! We pushed our way out, followed by hostile eyes, and for long afterwards we could still hear the flat notes of the hungry singers.

On again, and now the Jewish quarter. It was dark by this time. But here all was life and bustle, chaffering and shouting. The racial difference was staggering, but it was because the Jews worked day and night shifts to lose no time. The whole street was full from end to end of old clothes and rags. The air was heavy with the smell of food. I asked Mahler softly in his own words, ‘Are these our brothers?’ He shook his head in despair.

With a sigh of relief we at last turned a corner and found ourselves in a well-lighted street among our own sort of people. Can it be that there are only class and not race distinctions?"