DIFFUSION OF GASES WITHIN THE RESPIRATORY ORGANS. 237 



breathing is made more difficult, there is a slight increase. By inspira- 

 tion of compressed air the absorption of oxygen is increased to an ex- 

 ceedingly small extent. In order to give off one gram of carbon dioxid, a 

 smaller amount of air is needed at a low atmospheric pressure than with 

 a high barometer. There is no diminution in the excretion of carbon 

 dioxid on high mountains. The effects of artificially rarefied air and 

 of the rarefied atmosphere of high altitudes are not the same. A rare- 

 faction of air to 450 mm. of mercury still has no effect, the metabolic 

 changes proceeding unaltered. In the air of high altitudes metabolism 

 is increased, and respiration becomes more frequent and deeper. Ac- 

 cording to A. and J. Loewy and Zuntz the greater amount of light at 

 high altitudes is the exciting factor. 



12. In the presence of artificially induced dyspnea, as by tightly 

 compressing the thorax, the proteid metabolism is increased the amount 

 of urea being increased and there is an increase in the excretion of 

 oxalic acid, acetone, ammonia, and sulphur in the urine. 



Pathological. According to the experiments of Grehant on {logs, it -appears 

 that intense inflammation of the bronchial mucous membrane will diminish 

 the output of carbon dioxid, even if there be fever. 



In cases of diabetes the body is able to take up the necessary amount of 

 oxygen, but the quantity of carbon dioxid given off is diminished, and the respira- 

 tory quotient is low. 



Among the poisons, thebain increases the output of carbon dioxid, while mor- 

 phin, codein, narcein, narcotin, and papaverin diminish it. Curare lowers the 

 metabolism enormously, the absorption of oxygen falling about 35.2 per cent., 

 and the excretion of carbon dioxid about 37.4 per cent. Section of the spinal 

 cord has a similar effect. 



DIFFUSION OF GASES WITHIN THE RESPIRATORY ORGANS. 



In the pulmonary alveoli the air is richest in carbon dioxid and 

 poorest in oxygen. Further on, from the smallest bronchioles to the 

 larger ones and then onward to the bronchi and the trachea, the respired 

 air becomes, step by step, gradually more like the atmospheric air. 

 Hence it is that if the expired air of a respiration be collected in two 

 halves, the first half (coming from the larger air-passages) contains less 

 carbon dioxid (3.7 volumes per cent.) than the second half (5.4 volumes 

 per cent.). This inequality in the proportion of the gases at various 

 levels of the respiratory organs necessarily causes a continuous diffusion of 

 gases between the various levels, and also, finally, between the gases in 

 the larynx and nasal cavities and the outside atmosphere. The carbon 

 dioxid constantly diffuses from the depths of the air- vesicles toward the 

 outer air, while the oxygen of the latter diffuses toward the gaseous 

 mixture in the pulmonary alveoli. This diffusion is doubtless assisted 

 materially by the constant shaking of the respiratory gases by the 

 cardio-pneumatic movements. During hibernation, and also in cases 

 of apparent death of long duration, this must be the only means 

 for the exchange of gases within the lungs. Ordinarily, however, this 

 mechanism is insufficient for the respiratory process; so that the ex- 

 change of air produced by inspiration and expiration must be added to 

 it. By this latter means atmospheric air is introduced into those parts 

 of the lungs lying nearest to the large air-passages, from which and into 

 which the diffusion-currents of oxygen and carbon dioxid pass more 

 readily, on account of the greater differences in the tension of the gases. 



