Philadelphia a healthy city--Owing to the superior ventilation of its houses--But the theory of ventilation still imperfectly understood--About forty per cent. of all deaths due to foul air--The death rate for 1865--Expense of unnecessary sickness--In London--In Massachusetts--In New York--In Philadelphia--Consumption the result of breathing impure air--Entirely preventable--Infantile mortality--Report on warming and ventilating the Capitol--Copies of various tables therefrom--Carbonic acid taken as the test, but not infallible--The uniform purity of the external atmosphere--Illustrated by the city of Manchester--Overflowed lands unhealthy--Air of Paris, London and other cities--Carbonic acid in houses--Here we find the curse of foul air--Our own breath is our greatest enemy--Scavengers more healthy than factory operatives--Wonderful cures of consumption by placing the patients in cow stables--City buildings prevent ventilation, consequently are unhealthy--The air from the filthiest street more wholesome than close bed-room air--Unfortunate prejudice against night air--Dr. Franklin's opinion of night air--Compared with the instructions of the Board of Health, 1866--Sleeping with open windows--Fire not objectionable--A small room ventilated is better than a large room not ventilated--Illustration--Fresh air at night prevents cholera--Illustrated by New York workhouse--Dr. Hamilton's report--Night air just as healthy as day air--Candle extinguished by the breath--The breath falls instead of rises--Children near the floor killed first--Physicians' certificates do not state "killed by foul air"--Open fire-places are excellent ventilators--All fire-boards should be used for kindling wood--Illustration showing when ceiling ventilation is necessary. PAGE 3 LECTURE II.