364 ^- J- Anderson, 



Remarks. 



The lucid explanation given by D^- Charles of the more recent 

 work is mainly directed to the passage of oxygen into the blood, and 

 in this connection the exhalation of Carbonic acid suggests itself as a 

 question for discussion. The following facts bearing on the interchange 

 of gases may be collected and placed together. 



The air cells are enlarged in Inspiration and get small again 

 during Expiration, so that their walls (incl. the endothelial lining) get 

 thinner as the cells become thinner and broader. 



The blood pressure varies at different parts of the pulmonary 

 tract. The temperature of the blood in the capillaries of the lung is 

 probably affected by the lung-infundibula, and the evaporation of 

 water. 



The explanation commonly given, in former times, of the exha- 

 lation of Carbonic acid was that the moist cell membrane favoured 

 the passage outward of carbonic acid (A moist bladder full of carbonic 

 acid collapses in the course of a few hours if hung up, or placed in 

 a large stoppered jar). 



The carbonic acid is in a weak state of combination in the plasma, 

 and its departure is aided by the presence of the corpuscles, which 

 act thus like an acid (eg. phosphoric). 



Ordinary diffusion as distinguished from osmotic diffusion plays 

 an important part in the passage of gases through membranes. Hy- 

 drogen diffuses quickly. Oxygen more quickly than Nitrogen. Some 

 membranes, eg. a caoutchouc membrane, will thus keep back. Nitrogen 

 so well that the Oxygen that passes through will ignite a glowing 

 match. Several organic and inorganic substances absorb (and may 

 condense) large quantities of gases eg. Charcoal, Platinum (at a red 

 heat) Palladium (under 100^ C.) Caoutchouc &c. 



Although the tissues do not yield so favourable results as one 

 might expect, yet the conditions under which the experiments are 

 made are unfavourable. 



The presence of oxygen in air spaces in plants and the readiness 

 with which Carbonic acid is exhaled from free membranes (Intestine) 



