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L. R. Blinks 



measxireinent (as does the platinum polarographlc electrode in 

 contact with the tissue). The former, fluid type may be simply 

 a conventional glass electrode, plunged into the cell suspens- 

 ion (3), If only small amounts of material are available, or 

 one wishes to use a narrow beam of light (as from a monochromator 

 slit), a biolb of 015 Corning glass may be used to contain the 

 suspension. This may be spherical or elongated into a cylinder 

 as in the "everted" glass electrode employed by Blinks and 

 van Niel w). The bulb, filled with suspension, is inimersed in 

 an external buffer, with the pH changes now being recorded in 

 the opposite sense to the nonnal, inimersed electrode. Connect- 

 ions are made by calomel electrodes to the recording system 

 (a Beckman Type G meter and a "Speedomax" or "Servo-riter" 

 recorder. ) 



For thin thalli or membranous algae this system is not as 

 well adapted as the "film technique." Here the thallus is held 

 in direct contact with the glass surface, either with a band of 

 cellophane, or in the ultimate modification, by capillarity. 

 The former arrangement is immersed in sea water, exactly as with 

 the polarographlc platinum electrode. But this tended to give 

 slow responses; even when the volTime of sea water could be kept 

 small, CO2 equilibrated slowly with sea water by diffusion or 

 convection. Flow or stirring improved this situation (as with 

 the oxygen electrode). But, finally, with certain algae, the 

 arrangement shown in Fig. 1 was utilized. Some intertidal algae 

 such as Ulva , Enteromorpha or Porphyra are often exposed for 

 many hours to the moist air of the littoral zone, without obvious 

 damage or decrease of photosynthetic rate. Consequently it was 

 decided to try the alga in moist air only against the glass 

 electrode. The latter was largely coated with a hard wax 

 ("Ceresin") except for a "window" of about 3 mm. x 25 mm. Over 

 this glass sur-face was placed a moist, fresh thallus of Porphyra 

 or Ulva , and the electrode then mounted in a closed jar contain- 

 ing a little sea water at the bottom. The latter made contact 

 with a tab of the tissue which projected beyond the electrode; 

 this tissue, with resistance so much less than that of the glass 

 electrode, made essentially equal contact with all parts of the 

 exposed electrode surface. The fluid, consequently the total 

 buffering to be altered by CO2 exchange, was now reduced to that 

 in the tissue itself, plus the thin adherent films of sea water 

 on its inner and outer surface. As expected, the pH changes 

 were now much more rapid; also, the pH now reached a new steady 

 state determined by the photosynthetic rate, and the diffusion 

 of gaseous CO2 from the atmosphere. 



