““The consequences of dependence on the horse in 1870 involved negative externalities unrecognized by GDP, including manure and urine distributed on the streets and the cost of the unlucky laborers assigned to clean up the tons of horse waste, not to mention the diversion of a substantial part of agricultural production to feed the ubiquitous horses, in 1870 numbering 8.6 million, or roughly one horse for every five people.””
