Excerpt from An Introductory Lecture, Preliminary to a Course on the Institutes of Medicine: Delivered on the 9th of October, 1850, Before the Medical Class of the University of Pennsylvania The atmosphere is vitiated and contaminated in various ways. Respi ration is the most common. Accurate observations have established that from 4 to 5 per cent. Of carbonic acid is contained in the air expired by a. Male adult, and a somewhat larger per centage of oxygen has disappeared. The amount of air passing through the lungs in 124 hours, is about 400 cubic feet, which loses about 20 cubic feet of oxygen, and receives about 16 cubic feet of carbonic acid. The same air breathed three or four times becomes poisonous. One per cent. Of carbonic acid in the air, if breathed for some time, is prejudicial and death has been caused by a vitiation of not more than 12 or 15 per cent.

These facts show the importance of free ventilation to the preservation of health, and the free exercise of the functions, mental and physical.

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