706 PHYSIOLOGY OF RESPIRATION. 



gen to each 100 c.c. of blood instead of the usual 20 volumes. The 

 additional 8 volumes are contained in solution. Fish also are killed 

 when the oxygen pressure is increased to such a point that the water 

 contains 10 volumes of dissolved oxygen to each 100 c.c. In more 

 recent experiments by Smith,* made upon mice, it was found that 

 oxygen at pressures of 100 per cent, to 130 per cent, proves fatal 

 in a few days, the animals showing inflammatory changes in the 

 lungs. Oxygen at 180 per cent, kills mice and birds within twenty- 

 four hours. Pressures of two atmospheres of air (40 per cent. O) 

 have no injurious effect. No adequate chemical explanation can 

 be offered at present for this toxic action of oxygen at high tensions. 

 The matter is one of practical importance in connection with caisson 

 and submarine work and the therapeutical use of oxygen. 



Decreased Percentages of Oxygen. Numerous observers (Bert, 

 Zuntz, et al.) have shown that a fall in oxygen pressure has no 

 perceptibly injurious result until it reaches about 10 per cent. At 

 or somewhat below this pressure the hemoglobin is unable to take 

 up its full amount of oxygen, and the body consequently suffers 

 from a real deficiency in its oxygen supply, a condition designated 

 as anoxemia. According to Bert's experimental results, death with 

 convulsions quickly follows a fall of atmospheric pressure to 250 

 mms. (oxygen pressure, 50 mms. or 6 to 7 per cent.). Animals 

 supplied with an atmosphere containing a deficient amount of 

 oxygen show dyspneic respirations, which increase in violence 

 and finally become convulsive. 



Increased Percentages of Carbon Dioxid. It was pointed out 

 clearly by the researches of Friedlander and Herterf that death 

 from increased percentages of CO 2 is accompanied by symptoms 

 quite different from those due to lack of oxygen. As the CO 2 is 

 increased a noticeable hyperpnea may be observed (Zuntz) at a 

 concentration of about 3 per cent. When the concentration of CO 2 

 reaches 8 per cent, to 10 or 15 per cent, there is distinct dyspnea; 

 but beyond this point further concentration, instead of augmenting 

 the respirations, decreases them, and the animal dies, at concen- 

 trations of 40 to 50 per cent., without convulsions, but with the 

 appearance, rather, of a fatal narcosis. It is probable that in 

 these concentrations the CO 2 exercises a direct toxic action on the 

 nerve cells. 



High and Low Barometric Pressures, Mountain Sickness, 

 Caisson Disease, etc. High barometric pressures are used in 

 submarine work, diving, caisson work, etc. As stated above, it 

 follows from the work of Bert and Smith that when the pressure 



* "Journal of Physiology," 24, 19, 1899. 



t Friedlander and Herter, "Zeitschrift f. physiol. Chemie," 2, 99, 1878, 

 and 3, 19, 1879. 



