650 PHYSIOLOGY OF RESPIRATION. 



oxygen show dyspneic respirations, which increase in violence and 

 finally become convulsive. The ordinary symptoms described for 

 death from asphyxia are due, therefore, to the anoxemia, that is, 

 lack of oxygen, not to the accumulation of CO 2 . 



Increased Percentages of Carbon Dioxid. It was pointed out 

 clearly by the researches of Friedlander and Herter* 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. 



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 

 reaches 5 to 6 atmospheres long continuance in it may be followed 

 by injurious or fatal results due to the toxic action of the oxygen. 

 If the pressure is increased to 15 atmospheres the toxic influence 

 of the oxygen brings on death with convulsions. Practically, 

 however, such pressures are not encountered in submarine work. 

 A caisson is a wooden or steel chamber arranged so that it may 

 be sunk under water. The water is driven out by air under pres- 

 sure. Since the pressure increases 1 atmosphere for each 10 

 meters (33 feet), it will be seen that very high pressures of air 

 are not usually required. Caisson workers are at times attacked 

 by serious or even fatal symptoms, not while in the compressed 

 air, but during or after the " decompression " that is necessary in 

 the return to normal conditions. The symptoms consist of pains 

 in the muscles and joints, paralysis, dyspnea, congestion. Those 

 who have investigated the subjectf state that the injurious results 

 are due to a too rapid decompression. When this occurs the gases 

 in the blood, particularly the nitrogen, are suddenly liberated as 

 bubbles, which block the capillaries and thus produce anemia in 

 different organs. If the decompression is effected gradually no evil 

 results follow. 



The effect of low barometric pressures is chiefly of interest in 

 connection with residence in high altitudes, balloon ascensions, 



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

 and 3, 19, 1879. 



t See Bert, loc. cit., p. 939; also Hill and MacLeod, "Journal of Physi- 

 ology," 29, 382, and "Journal of Hygiene," 3, 407. 



