Recent Progress in Sanitary Science. 211 



the amount of carbonic anhydride in the ground below the 

 surface, was much greater than that above, and that it in- 

 creased with the depth and varied with the season, being 

 least in winter and greatest in summer. His object was 

 similar to that in view in the determination of the carbonic 

 anhydride in ill-ventilated buildings, that of obtaining a 

 measure of the " impregnation " of the ground with organic 

 impurities, by the oxidation of which the carbonic anhydride 

 is produced. It is analogous to the determination of the 

 nitric and nitrous acids in drinking water, bodies not of 

 themselves detrimental in minute quantities, but important 

 as affording a measure of the previous pollution of the water 

 by nitrogenous excreta, etc., from the oxidation of which 

 they are derived. The examinations of Dr. Nichols, which 

 were conducted upon the made lands of the " Back Bay " of 

 Boston, showed that there was very little difference in the 

 amount of carbonic anhydride at different depths during 

 most of the period occupied by the experiments ; but in 

 October, November, and December, it had increased sensibly 

 at a depth of ten feet, above its amount at a depth of six 

 feet. This curious result, which agrees with Pettenkofer's, 

 he attributes to the diffusion of the carbonic anhydride from 

 the surface, and to the increased rapidity of this diffusion Avhen 

 the temperature of the air falls below that of the ground. 



With regard to ventilation itself, as an art, repeated fail- 

 ures, often with grave results, by architects of great promi- 

 nence, are at last convincing the public that the ventilation 

 of buildings constructed on different plans, of different ma- 

 terials, with different uses, and located differently in respect 

 to air, wind, and sun, is an art of great difficulty ; one not 

 to be practised on occasion by the hospital-physician, the 

 school-trustee, the alms-house inspector, the engineer, or 

 even the architect, as a subject popularly supposed to be 

 fully understood by every well-informed person, but should 

 be placed in charge of persons making the heating and ven- 

 tilating of buildings their especial study. 



