THE CONTROL OF THE RESPIRATION 375 



methods have been employed in the investigation of this subject. The 

 most important of these are as follows: (1) Breathing from a tank con- 

 taining varying mixtures of oxygen and nitrogen (Dreyer apparatus). 

 This apparatus was used extensively in the British Army in testing the 

 ability of candidates for the aviation service to withstand low oxygen. 

 Its greatest value is that the alteration in oxygen content of the inspired 

 air can be made either gradually or quickly. (2) Breathing from a 

 tank, through valves which direct the expired air to pass through 

 an apparatus for absorption of the C0 2 , after which it re-enters the tank. 

 The subject, therefore, re-breathes the air of the tank from which he 

 gradually absorbs the oxygen. In this method the 2 -content of the 

 inspired air falls gradually, and effects are produced which must be 

 similar to those which would be caused by slow ascent to higher alti- 

 tudes. The rate at which the 2 falls can be varied by altering the size 

 of the tank. When a very rapid fall is desired rubber bags can be used 

 in place of tanks. An apparatus on this principle was employed for 

 testing aviators particularly in the United States Army. (3) Breathing 

 in an air-tight cabinet containing properly arranged soda lime absorbers 

 to take up the C0 2 , the oxygen decreases at a rate which is inversely 

 proportional to the size of the cabinet. (4) Breathing in a strongly 

 built steel chamber connected with a powerful pump by means of which 

 the chamber can be partially evacuated and the pressure maintained at 

 any desired level. Such a chamber has been used by Haldane, Kellas 

 and Kennaway in important experiments, the results of which we shall 

 consider immediately. (5) Adding a sufficient percentage of carbon mon- 

 oxide gas to the inspired air. This combines with the hemoglobin of the 

 blood and renders this incapable of carrying the oxygen. 



The observations made by the use of these methods have been com- 

 pared with those made during life at high altitudes, particularly in con- 

 nection with mountaineering. The latter observations are of particular 

 importance in the study of the adaptive processes which come into play 

 to render persons who have become accustomed to high altitudes immune 

 to the distressing symptoms from which others suffer. 



There is considerable variability in the reactions of different persons to 

 decreased oxygen. These symptoms are partly subjective and partly ob- 

 jective in nature and they show slight differences according to whether the 

 anoxemia is produced by a lowering of barometric pressure (decom- 

 pression), or by simply reducing the percentage of oxygen in the inspired 

 air. In the former case there is also a slight difference between the symp- 

 toms following decompression in an experimental chamber, and those 

 observed on a high mountain. In a general way the symptoms are less 



