New York City had one of the highest concentrations of horses in the country. By 1880, there were more than 100,000 horses in the city, and each one produced between 15 and 35 pounds of manure and urine. Residents of wealthier areas could afford to hire people to cart street refuse away, and had their houses connected to new sewers. However, entire neighborhoods were notorious for their noxious odors, such as the Five Points (built on top of the poorly-filled Collect Pond, many wooden tenements sank, and most of them had haphazardly built outhouses that overflowed when it rained, flooding basement apartments and the surrounding streets with fecal matter) and the Gaslight District (the first tanks were built in 1842, and often leaked, soon the neighborhood was populated by immigrants; this area is now taken up by Stuyvesant Town, Peter Cooper Village and Gramercy). When it rained heavily or snowed, street refuse was mixed up and carried throughout the streets; in warm weather, it baked in the streets.

These conditions reached a crisis in the 1870s, when an equine virus killed hundreds of horses a day, left to rot in the street for weeks (imagine what an impediment to traffic that was!). Of course, this added to the foul smells of the city, which frustrated city residents. The police were assigned to street cleaning patrols beginning in 1872, and in 1881 the Department of Street Cleaning was formed, headed by George E. Waring, who required cleaners to sweep by hand and wear crisp white uniforms, earning them the nickname "white wings." Waring also established the city's first recycling system in 1895. Along with the rise in public health awareness, increased advances in sanitation helped increase the quality of life of many New Yorkers. The horses were housed in the hundreds of stables and carriage houses across the city. Rather quickly, many of these stables found themselves obsolete as the car became more popular; in 1910 there were more than 128,000, but by 1920 there were 56,000. The last horsecar lines ran on Bleecker Street until 1917 and West Street until 1918, when electrified trolleys took over.

Of course, New York City, as anyone who has visited knows, has some very distinctive smells. During the summer, trash bags pile up on sidewalks, and where they've been broken into by rats trash and fetid ooze drips down the street and bakes there. The rivers at low tide are also particularly pungent, and the rocks are covered with a sickly brown-green mud that smells of sour saltwater. For the intrepid explorer, the stretch of Central Park South and lower Central Park is notoriously foul, as that is where the horse-drawn carriages congregate (in places, the streets are slick with manure). It certainly is not as bad as it was in the past, and you can move a few blocks away and not have to deal with some of the smells, but if you go to the right places you can definitely experience a bit of the olfactory past.