THE INFLUENCE OF CHEMICAL FACTORS 



81 



animals that the oxygen consumption is independent of the oxygen 

 pressure of the surrounding medium when there is a positive tension 

 of the gas in the tissues of the organism, and that the oxygen pressure 

 becomes the limiting factor only when the oxygen supply fails and 



Rfiahvc 



5 10 15 20 25 30 35 40 45 50 55 60 65 79 75 80 85 90 93 100 %% 



in air 



FIG. 21. Relation between oxygen pressure and oxygen consumption. After Thunberg. 



the oxygen tension in some of the tissues becomes zero. This conclu- 

 sion is obviously hypothetical, however, and experiments will have to 

 be made in which the oxygen consumption is directly compared with 

 the oxygen tension in the tissues themselves. 



Toxic EFFECTS OF HIGH OXYGEN PRESSURES. 



High oxygen pressures appear to have the same effect on cold- 

 blooded animals as on warm-blooded. Lehmann [1883, 1884] has 

 made a number of experiments on frogs and on organs of frogs and 

 snails. He found that oxygen compressed to 10 to 14 atmospheres kills 

 these animals with symptoms which are similar to asphyxiation. At 

 low temperatures a considerable power of resistance is shown against 

 high oxygen pressures. The animals become paralysed but may re- 

 cover even after thirty hours' exposure. When the animals are rapidly 

 decompressed gas bubbles are liberated in the tissues as well as in the 

 blood, which shows that the oxygen tension must become very high 

 everywhere within the organism. 



Flitter [1904] has found that the action of oxygen on certain 

 protozoa becomes harmful at quite low pressures. Spirostomum am- 

 biguum, for instance, shows negative chemotaxis against air, and 



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