476 Professor William Stirling [March 4 



viz. carbon dioxide, is got rid of. Closure of the wind-pipe, even for 

 a few minutes, brings death with it from suffocation. The entrance 

 of oxygen is prevented and the escape of carbon dioxide is arrested. 



The process of breathing is common to all living beings — to j^lants 

 and animals alike. It consists essentially in the consumption of 

 oxygen by the tissues and the giving out of carbon dioxide. It is 

 immaterial whether the animals or plants live in water or air, the 

 principle is the same in both cases. Living active protoplasm 

 demands a supply of oxygen. 



All the world 's a stage. The human body is at once a stage and 

 a tabernacle — a vast theatre — and the myriads of diverse cells of which 

 it is composed, the players. 



The cells or players, as active living entities, not only require food 

 but they require energy. The respiratory exchanges in and by the 

 living cells provide the energy for the organism. This breathing by 

 the cells is called " internal respiration." In a complex organism, 

 therefore, the respiratory exchanges represent the algebraic sum of 

 the respiratory activity of the several tissues that make up the 

 organism. The various tissues, however, breathe at very unequal 

 rates. 



In one of his charming " contes philosophiques," Voltaire describes 

 the visit of a giant of Sirius to our planet. Before reaching his 

 journey's end he would have to traverse an aerial medium ; and on 

 arriving would see before him a fluid medium in continual movement, 

 and tracts of solid land. After investigation — or no doubt he would 

 be told, even though he was not personally conducted — that the water 

 surface of this our globe is two and a half times greater than the 

 land surface. He would discover that there are animals that live in 

 air, others in water, and again others on land. Our visitor would find 

 out that the respirable media are two — water and air —and that there 

 are 210 parts of free oxygen in a litre of air, while there are only 

 3-10 dissolved in a litre of water. 



Had Voltaire's friend paid us another visit during the present 

 century, we should be able to tell him that the water of the Thames 

 above London contains 7 * 40 c.c. of per litre ; at Woolwich only 

 • 25 ; the decrease being due to the pollution of the river. Putting 

 it broadly, water contains only 3-10 parts per litre, while air contains 

 210. Water-breathers under good conditions have twenty times less 

 than air-breathers. It is as if air-breathers on land had the per- 

 centage of O2 reduced to 1. 



He would also be told that carbon dioxide — CO2 — is also remark- 

 ably soluble in water, and readily combines with certain bases present 

 in water; thus water forms an admirable medium into which an 

 animal may discharge its effete and poisonous irrespirable CO^. 



He would also be told that our blood contains 60 volumes per 

 cent, of gases, and that there is more and less CO2 in arterial blood 

 than in venous blood. 



Perhaps the name of Sir H. Davy might be whispered to him, for 



