EXPERIMENT STATION BULLETINS. 473 



through lecithin, lecithin-lard and lanolin membranes. The lecithin-lard 

 mixture was made of about equal parts of lecithin and lard thoroughly 

 mixed together. In half of these both methods mentioned were run to 

 gether — i. e. the method of total gas-volume measurements, and the 

 method of percentage determinations of the oxygen, gasoline-vapor, etc., 

 present at the start and the end of each separate test in the series. The 

 cautionary checks were also observed. Four series of tests were run to 

 determine the influence of chloroform-vapor upon the rate of oxygen 

 transfer through lecithin membranes. These four series of tests were 

 carried out by the one method only — namely, that of the total gas- 

 volume measurements at the beginning and end of each test. 



The results of all the experiments by both methods pointed directly 

 to the conclusion that, in the presence of gasoline-vapor air or chloro- 

 form-vapor air, the membranes named permitted less oxygen to pass per 

 unit of time than they permitted in air only. 



Note that the experiments with the covered preparation dish of lime- 

 sulphur were carried out under the conditions encountered regularly by 

 the tissue cells of an insect subjected to fumigation by gasoline-vapor or 

 chloroform-vapor. Just as oxygen reached the lime-sulphur for absorp- 

 tion at a lower rate, when passing through the lecithin membrane in 

 the presence of gasoline-vapor or chloroform-vapor, so, it may be judged, 

 less oxygen would be able to reach the oxygen-absorbing protoplasm of 

 the cells through the surrounding body fluids (blood) etc., the lipoids of 

 which held gasoline-vapor. So also, in the presence of air containing that 

 vapor, less oxygen would be able to pass through the surface of an 

 insect-tissue extract (containing hydroquinone, for example) into the 

 extract where it could be utilized by the oxidase in oxidizing hydro- 

 quinone. 



Now, the actual percentage of oxygen present in the gasoline-vapor air 

 would naturally be lower than in normal, pure air through dilution by 

 the gasoline-vapor, but it appeared that this alone could not fully account 

 for the lower rate of oxygen transfer through the membranes. Attention 

 may be called to the fact that when the percentage of oxygen in the air 

 of the container, for the "air only" tests, was made as nearly equal as 

 possible to the percentage of oxygen in the gasoline air used (see Nos. 

 3 and 4, Table Vll), the rate of oxygen transfer through the membrane 

 remained lower, nevertheless, in the presence of gasoline-vapor. In Exp. 

 3 (Table Vll) the oxygen percentage was 20.2 at the beginning, and 

 18.26 at the end of test No. 1. In test No. 2, carried out in "gasoline- 

 vapor air" mixture, 18.26 per cent oxygen was present at the start and 

 17.5 per cent, at the end. Test No. 3 of Exp. 3 was started after the 

 covered preparation dish had been aired several hours. All the gasoline 

 had not been given up by the membrane, however — and by the end of 

 the test, the small percentage of gasoline-vapor show^n in the table had 

 been given off to the air of the container. A very thick lecithin-lard 

 membrane had been used. In Exp. 4 (test No. 1) of the same table, the 

 percentage of oxygen at the beginning was 15.13, and at the end, 13.2. 

 In test No. 2 of this experiment, the gasoline-vapor air contained 14.6 

 per cent oxygen at the start, and 13.11 per cent at the end. The con- 

 clusion in regard to this point must be, therefore, that the gasoline-vapor 

 which was taken up by the membranes rendered them less permeable to 

 oxygen. Eepresentative results are given in Table VII. 



