A Discussion on the interchange of Gases in the Lungs. 365 



shows how readily a gas may be disposed of, if a tissue were super- 

 saturated, or contained a gas at a high tension. 



Simple absorption of gases by fluids may be given as an expla- 

 nation of absorption of some gases by tissues, but does not account 

 for amount of Carbonic Acid and Oxygen in the blood. 



Weak chemical combination, or a close adhesion of the gas to a 

 chemical compound might be illustrated by the force of cohesion that 

 exists in solids. 



The greed which living substances manifest for oxygen, and various 

 other substances of nutritive value, leads to a motion of the living 

 substance or a flow of the gas. 



The supersaturation of a tissue might result from a change in 

 the tissue itself. It is clear that a suitable safety resevoir would be 

 of great importance to fishes in such a case. Pure oxygen will tend 

 to paralyse a tissue. 



The amount of Haemoglobin in the blood is affected by many 

 circumstances (Von Lesser) tying the animal in the recumbent position 

 produces a transitional increase and decrease. 



Numerous tissues separate substances already formed in the blood 

 eg. the kidneys. 



This suggests a means by which oxygen might reach the blood 

 from the air cells. 



A membrane might by altering in composition, in part, after the 

 absorption of a gas cause a discharge of the same gas. 



The lung air passages in a mammal may be divided into three 

 parts, 



a) the part into which air from without is freely admitted, 



b) the part which is devoted to the rythmic air current of resi- 

 dual air, and 



c) the portion which contains the slowly flowing air. 



Diffusion tends to equalize the composition of the air in the 

 different sections, but the expansion of the alveoli leads to a rari- 

 faction of the air, as the aperture leading into an infundibulum is 

 about or 1 mm. or a little more. After expansion the walls of the in- 

 fundibulum compress the air at flrst, this is due to the too small 



