EFFECTS OF CHANGES IN AIR BREATHED 1099 



the blood is already insufficient, marked amelioration of the symptoms may be produced 

 by inhalation of pure oxygen. Especially is this noticeable where there is failure of 

 the heart. In these cases the heart, already affected, is unable to keep up an adequate 

 circulation and to supply itself with sufficient oxygen. A vicious circle is thus estab- 

 lished in which the heart tends to get steadily worse. By administration of oxygen an 

 adequate supply of this gas to the heart-muscle is assured ; the heart-beat therefore 

 becomes more effective and the whole circulation is improved and therewith the pro- 

 vision of oxygen to the body at large. 



If a warm-blooded animal be immersed in a chamber and submitted to 

 pure oxygen at a pressure of four atmospheres, it dies as rapidly as if it were 

 in an atmosphere of pure nitrogen. At this pressure the oxidative processes 

 of the body as well as the intake of oxygen into the lungs are absolutely 

 abolished. It is interesting to note that certain other oxidative phenomena, 

 e.g. the spontaneous oxidation of phosphorus, also cease if the tension of the 

 oxygen be sufficiently high. Exposure of an animal over a considerable 

 period of time to a pressure of oxygen of two atmospheres may, as Haldane 

 and Lorrain Smith have shown, set up severe inflammation of the lungs and 

 thereby cause death indirectly. 



CHANGES IN TENSION OF OXYGEN. If a man breathe a mixture of 

 nitrogen and oxygen free from carbon dioxide, and the oxygen be gradually 

 diminished, no feeling of ' want of breath ' may be experienced. With per- 

 centages of oxygen as low as 12 per cent, there may be no change in the 

 breathing, even though the deficient oxygenation of the blood may be 

 shown by the blueness of the lips and face. If the oxygen be reduced still 

 lower, a certain amount of hyperpnoea may occur, but in many cases the 

 individual experimented on may not feel any ill effects until he suddenly 

 becomes unconscious from lack of oxygen. If fresh oxygen be not supplied 

 this unconsciousness may be followed by convulsive movements and death. 

 If the administration of low percentages of oxygen, e.g. about 10 to 12 

 per cent, of an atmosphere, be continued for some time, the subject of the 

 experiment may suffer considerable discomfort. One of the signs of oxygen 

 lack is often severe headache, and this may be accompanied by vomiting or 

 nausea and by a feeling of discomfort in the precordial region. Many 

 experiments have been made both on animals and man by submitting them 

 to a lowered atmospheric pressure in chambers specially built for the 

 purpose. The limit to which the pressure may be reduced varies in different 

 individuals, the variations being determined by the type of respiratory 

 movement of the individual in question, since on the depth of respiration 

 depends the relation between the tension of oxygen in the alveoli and that 

 in the inspired air. The lowest limit at which life is possible corresponds 

 to an oxygen tension in the alveoli of 27 to 30 mm. Hg. 



MOUNTAIN SICKNESS. The phenomena just described as ensuing on 

 exposure of an animal to low oxygen tensions in a respiratory chamber for 

 some length of time are exactly similar to those which' are regarded as 

 characteristic of mountain sickness. The following Table shows the diminu- 

 tion in the atmospheric pressure at varying heights above the level of the 

 sea : 



