690 PHYSIOLOGY: J. F. McCLENDON 
sea varied from about 0.03-0.05% of an atmosphere, but these meas- 
urements will be made more accurately next summer. One estimation 
of the CO2 of the air was 0.033%. It seems probable that CO2 is pass- 
ing from the sea to the air at Tortugas, but this question also will 
be studied more accurately next summer. From Fox's data and the 
above measurements, the following estimations at 30° may be made: 
CO2 content in cc. per litre of sea water . 
CO2 tension in percent of an atmosphere. 
PH 
44.5 46.25 47.5 
0.03 0.04 0.05 
8.22 8.15 8.1 
From this table the CO2 content may be estimated from the PH and 
hence in respiration may be made by estimating the PH of water con- 
taining animals, at certain periods. For this reason rapid methods of 
estimating the PH were calibrated by comparing vials of Sorensen*s 
borate mixtures colored with thymolsulphonephthalein^ with a similar 
vial of sea water to which is added the same quantity of thymolsulphone- 
phthalein, and the PH read off colorimetrically. It was found that 
when the sea water was tested with the same hydrogen electrode used 
in standardizing the borate mixtures its PH was found to be 0.3 lower 
than that estimated colorimetrically, owing to the salt action on the 
indicator, consequently 0.3 must be subtracted from the result obtained 
colorimetrically. The salt error could not be determined more accu- 
rately with these tubes since they read down only to 0.1 on the PH 
scale but I understand that Lubs and Clark are studying this question 
in detail and may have more exact data. 
Some general experiments on the physiological significance of the 
ions of sea water were made, but since they were intended to be gen- 
eral, no extremely exact quantitative data were recorded. Hence these 
experiments cannot be compared with those of A. G. Mayer on the 
same subject in which he has made some exact determinations of the 
effect of H and OH ions at various concentrations. Since I have shown 
that ions may change the permeability of irritable cells, and excitation 
seems evidently to be associated with increase in permeability to ions 
and I have also shown that it is accompanied by increase in electrical 
conducitivity; the question arises whether all ions may be divided into 
two classes: those which increase permeability and those which in- 
hibit this change. Experiments on the pulsation of the jell}^ fish, 
Cassiopea, and the heart of the Conch, S trombus, indicate that OH', Na', 
and K' increase permeability, and that H*, Mg' *, and Ca* ' inhibit 
increase in permeability. Since a certain increase in permeability 
puts the cell in the stimulated condition which is the same as the re- 
