136 AIR AND LIFE. 



Apparent uselessness of this gas; Its negative character; Essential role of nitrogen 

 compounds in plant life; Role of atmospheric nitrogen; Direct proofs of the absorp- 

 tion of this gas by plants; Mechanism of this absorption; Role of some microorgan- 

 isms in the assimilation of atmospheric nitrogen; Experiments upon legnmiuous 

 plants by Nobbe, Hellriegel, and Willfarth; Practical consequences; Inoculation of 

 soil or of plants; Role of some plants which prepare nitrogen for others; Melcbior 

 Treub's observations at Krakatoa; Role of carbonic acid; Its toxicity for animal 

 organisms ; Proportions of this gas which are harmful ; Observations and various 

 analyses ; Quantity of pure air which is required per hour and per individual ; Exam- 

 ples of intoxication and death by carbonic acid; " Valleys of Death ; " Carbonic acid 

 beneficent during the death struggle ; Important role of this gas in the life of plants, 

 it is the source of their carbon, and if it disappeared life would become extinct. 



IV. — Biological Role op Air Physically Considered. 



Atmospheric pressure; Effects of gradual decrease of pressure; Mountain sickness, 

 its nature and cause; Incipient asphyxia; Variability in different organisms and 

 conditions of sensitiveness to altitude; Causes of this variability; Experiment by 

 P. Regnard upon the role of fatigue and muscular exercise in the production of 

 mountain sickness; Effects of sudden decrease of pressure; Internal injuries, their 

 mechanism; Accidents to divers, etc.; Effects of increase of pressure due to toxic 

 effect of oxygen ; Adaptation to altitudes; Mechanism; Increase of the respiratory 

 capacity of the blood; Experiments of Paul Bert, Viault, Muntz, Regnard; Beneficent 

 effects of the moderate altitude ; Movements of the atmosphere ; Role in the purifica- 

 tion of air; In mixing the constituents; In disseminating vapor and heat; In the 

 dispersal of species, In leveling the surface of the soil; Possibility of using the 

 energy of wind for industrial purposes; Plans and experiments; Max Plessner and 

 S. P. Langley; Biological role of substances suspended in atmosphere; Of aqueous 

 vapors ; Of mineral dust ; Of aerial organisms and microbes ; Air carries life and death 

 in it; It is an element essential to life, and is made with the elements derived from 

 living or dead organisms; Circulation of matter. 



