AIR AND LIFE. 165 



an average adult retains over 740 grams, or 510,500 cubic centimeters, a 

 total amount of 500,000,000 cubic meters per day for the wliole of man- 

 kind. The amount of oxygen required varies somewhat according to 

 sex and age within the limits of the same species. During childhood 

 and old age less is needed than during the prime of life. An adult may 

 require 910 grams in twenty-four hours; an 8-year old child is content 

 with 375. Various circumstances, such as vigor, health, temperature, 

 rest, exercise, and so on, increase or diminish oxygen consumption. 

 This oxygen is absorbed in our tissues, which it reaches chiefly through 

 the agency of the lungs and blood; a small proportion, however (one- 

 eightieth of the amount absorbed by the lungs), is absorbed by our 

 skin, which has, therefore, some respiratory importance. 1 All our 

 tissues need oxygen ; all breathe. For it must not be forgotten that the 

 lung is nothing more than an instrument in the respiratory process; the 

 chemical operation which is the essential part of this function takes 

 place elsewhere, in the tissues themselves. The lung is only the door 

 by which oxygen enters the system. Physiologists held quite different 

 views a century ago, and Lavoisier himself supposed that the main 

 act of respiration takes place in the lung. What really happens is 

 that oxygen, introduced into the lung, filters through the very thin 

 Avails of the pulmonary capillaries, where it finds in the red blood cor- 

 puscles a substance called hemoglobin, with which it unites to form a 

 compound which bears the name of oxyhemoglobin. A very unstable 

 compound it is, for throughout the tissues, in the capillary vessels of 

 the whole body, oxygen is allowed to escape and effect its work among 

 the cells. Numerous and complex reactions take place, and one set 

 of them results in the formation of carbonic acid. The blood, therefore, 

 is nothing more than a vehicle; it carries oxygen to the tissues and 

 brings back to the lungs carbonic acid, which, if not allowed to escape, 

 would soon cause death. The "orgauic combustions" do not occur in 

 the lungs, as was thought a century ago; their seat is in the tissues, 

 throughout the whole body. 



While respiration is common to all animals, it is not equally active 



been devised by Prof. Charles Richet in order to give an experimental proof of the 

 soundness of tbis inference. All that is required is an india-rubber tube, some 

 2 or 3 yards in length, of ratber wide bore. Tbis tube is so adapted to tbe respira- 

 tory apparatus of a dog or rabbit, that by some means or other he is made to 

 breathe through it. Under such conditions death from asphyxia soon results. 

 This experiment merely exaggerates the normal conditions; adding the tube 

 amounts to nothing more than lengthening the air passages, and putting a greater 

 distance between the lung and the atmosphere. The result is not a matter of sur- 

 prise — external air can not reach the lungs. Inspiration is not sufficient to draw to 

 the lung the whole of the air contained in the tube, plus a sufficient amount of pure 

 air. Each inspiration introduces some fresh air in the end of tbe tube, each expi- 

 ration expels it, and none reaches the animal, which is unceasingly breathing the 

 SE.ine air over again and perishes from asphyxia, although in appearance breathing 

 as freely as possible. 



'Cutaneous respiration is quite sufficient, in winter, to maintain life in some 

 animals; the frog, for instance. 



