ADVERTISEMENT. 



The present ineiiioir is the result of a series of investigations made 

 by Doctoi's J. S. Billings and IS. Weir Mitchell, assisted by Doctor D. H. 

 Bergey, under a grant from tlie Hodgkins Fund of the Smithsonian 

 Institution, for the [nii'pose of determining the- nature of the peculiar 

 substances of organic origin contained iu the air expired by human beings, 

 with special refei-ence to the practical application of the results obtained 

 to problems of ventilation for inhabited rooms. 



In accordance with the rule adopted by the Smithsonian Institution 

 the work has been sul)mitted to a committee, in the present instance con- 

 sisting of Doctor H. C. Wood, Professor William H. Welch, and Professoi' 

 Charles S. Minot, and having been recommeuded by them for publication, 

 it is herewith presented in the series of Contributions to Knowledge. 



S. P. LANGLEY, 



SECKETAKY. 



Washington, November, 1895. 



HI 



