TRANSACTIONS OF SECTION I. 807 



2. On an Aerotonometer and a Gas-burette.^ 

 By Professor L^ON Fredericq, Liege. 



The air wbich enters the lung is rich in ox^-frcn (20-9 per cent.) and poor in 

 carbonic acid (0'03 per cent.). On leaving the lung it is relatively poor in oxygen 

 (18 per cent, in dogs) and rich in carbonic acid (2 to 3 per cent, iu dogs). It has 

 given up oxygen to the blood and received from it carbonic acid. 



What is the cause of this gaseous exchange between the blood and the air of 

 the pulmonary alveoli ? Pfliiger believed that he had succeeded in explaining 

 this exchange by the simple laws of gaseous diffusion — laws in virtue of which 

 each gas passes from a medium in which its tension is high towards a medium in 

 ■which its tension is low. The determinations of carbonic acid ten.^ion made by 

 Pfliiger's pupils simultaneously in the blood by means of the aerotonometer and in 

 the air of the pulmonary alveoli were in complete harmony with this explanation. 



Christian Bohr has come to a different conclusion on this subject. According 

 to him, gaseous diffusion alone does not explain the exchange of g.ises between 

 the blood and the air of the lung. Bohr has found in several of his experiments 

 the air of the alveoli richer in oxygen and poorer in carbonic acid than in the 

 arterial blood leaving the lung. According to Bohr, the tissue of the lung plays 

 an active part in respiration : the pulmonary epithelium excretes carbonic acid by 

 a true secretion process, and passes oxygen into the blood, not in accordance with 

 the laws of diffusion, but against these laws. 



I have recently taken up this subject again, and in doing so have made use 

 of the aerotonometer exhibited to the Section, which is a modification of the 

 instrument of Pfliiger. The apparatus consists essentially of a sufficiently long 

 vertical tube, connected above with the carotid of a living animal (an anacstbetised 

 dog), and below with a vein. The arterial blood (which has previously been 

 rendered incoagulable by the injection of propeptone) flov/s continuously over the 

 inner surface of the tube of the aerotonometer, which is kept at a temperature of 

 o8° C. If the experiment lasts sufficient time for tlie attainment of equality of 

 tension of the gases of the blood and those enclosed in the aerotonometer, an 

 analysis of the latter gases will indicate the tension of the gases of the blood. 

 Bohr believed that equality of tension could be reached in a few minutes, and 

 thus obtained erroneous results. I have found that nearly two hours are necessary 

 before equality of tension is reached. One finds then that the air of the aerotono- 

 meter contains 2 to 3 per cent, of carbonic acid and 12 to 14 per cent, of oxygen, 

 representing the tension of these gases in the blood in accordance with the 

 diffusion theory. I have also found that if one lets the animal breathe pure or 

 nearly pure oxygen, the tension of this gas in the arterial blood may exceed 

 GO per cent, of an atmosphere. The animal, nevertheless, shows only a slight 

 tendency to apnoea ; it continues to breathe. Apnoja is thus not a necessary 

 result of a very high oxygen tension in arterial blood. This is a fact which seems 

 to me very important in connection with the theory of apnoea. 



The gas analyses were made with a gas-burette, shown to the Section, which 

 is simply a modification of that of Hempel. The burette is drawn out at the level 

 where the readings are made, so as to permit of reading easily to '02 or '01 c.c. 

 The confining liquid is water (and not mercury), which gives rise to scarcely any 

 error, diffusion of gases into liquids being so slow. The carbonic acid is absorbed 

 by potash solution, the oxygen by phosphorus. 



3. On Local Immunity. (A Preliminary Communication.)'^ 

 By Louis Cobbett, M.A., M.B., F.R.C.S., and W. S. Melsome, M.A., M.D. 



If it be true, as there seems reason to believe, that recovery from an infectious 

 disease is due to certain changes in the body, which make it more resistant to the 

 micro-organisms which cause that disease, and that the same changes are also the 



' For further details see Centralhlatt fdr Physiologie, 1893, vii. p. 26; 1894, viii. p. 34. 

 * A full report is published in the Journal of Pathology, 1894. 



