584* POPULAR SCIENCE MONTHLY. 



increases and the demand for it becomes more urgent. The pro- 

 portion of increase of carbonic acid and of diminution of oxygen 

 which has been found to exist in badly ventilated churches, 

 schools, theaters, or barracks is not sufficiently great to account 

 for the discomfort which such conditions produce in many per- 

 sons, and there is no evidence to show that such an amount of 

 change in the normal proportion of these gases has any influence 

 upon the increase of death-rates which statistical evidence has 

 shown to exist among persons living in crowded and unventilated 

 rooms. It has been well established by observation and statistics 

 that tuberculosis and pneumonia are the diseases most prevalent 

 among persons living and working in unventilated rooms. But 

 consumption and pneumonia are caused by specific bacteria, which 

 for the most part gain access to the air passages by adhering to 

 particles of dust which are inhaled, and it is probable that the 

 greater liability to these diseases of persons living in crowded and 

 unventilated rooms is to a large extent due to the special liability 

 of such rooms to become infected with the germs of these diseases. 



The discomfort produced by crowded, ill- ventilated rooms in 

 persons not accustomed to them is not due to the excess of car- 

 bonic acid, nor to bacteria, nor in most cases to dusts of any 

 kind. The two great causes of such discomfort, though not the 

 only ones, are excessive temperature and unpleasant odors. The 

 cause of the unpleasant, musty odor which is perceptible to most 

 persons on passing from the outer air into a crowded, unven- 

 tilated room is unknown; it may, in part, be due to volatile 

 products of decomposition contained in the expired air of per- 

 sons having decayed teeth, foul mouths, or certain disorders of 

 the digestive apparatus, and it is due in part to volatile fatty 

 acids given off with, or produced from, the excretions of the skin. 

 The results of this investigation, taken in connection with the re- 

 sults of other recent researches, indicate that some of the theories 

 upon which modern systems of ventilation are based are either 

 without foundation or doubtful, and that the problem of securing 

 comfort and health in inhabited rooms requires the consideration 

 of the best methods of preventing or disposing of dusts of various 

 kinds, of properly regulating temperature and moisture, and of 

 preventing the entrance of poisonous gases, like carbonic oxide 

 derived from heating and lighting apparatus, rather than upon 

 simply diluting the air to a certain standard of proportion of car- 

 bonic acid present. 



It would be unwise, however, to conclude from the facts given 

 in this report that the standards of air supply for the ventilation 

 of inhabited rooms, which are based on the results of Pettenkofer's 

 work, are too large. 



