3. By superposing spectral flashes upon steady adapting lights it is possible to find a spectral range in which only one kind of cone is effective. In this range the effect of any spectral light may be matched with that of any other provided the energies are linked in a fixed ratio that defines the action spectrum of the pigment.4. The green pigment has an action spectrum with maximum at 540 nm and corresponds well with the pigment that Marks measured in 'green' cones. The blue pigment has not been measured, but it probably corresponds with that found by Marks in 'blue' cones. However, the red pigment whose action spectrum we measured had its maximum at 680 nm, whereas the difference spectrum of Marks's red cone pigment peaked at 620 nm. The 620 nm cones excite the luminosity S-units but not the R/I units.5. In the range where only one type of cone is effective the relation between the light intensity, Io, and V0, the S-potential generated (both expressed in suitable units), is given by equation (1) p. 545. It is the relation that would be found if cone signals increased the conductance through a polarized 'S-membrane' in proportion to the flux of caught quanta.

SUMMARY1. S-potentials were recorded in fish from units which never responded by depolarization. These hyperpolarizing units are the L-units of Svaetichin & MacNichol (1958).2. Figure 5 shows some sets of action spectra from a single unit. For each curve the criterion of action was hyperpolarization to a fixed level, by lights of various wave-lengths. When these lights fell upon zero background (circles) the curves show that two kinds of cone contribute to the action spectrum, one with the 620 nm pigment of Marks and one with the 680 nm pigment of Naka & Rushton (1966a).3. When the lights fell upon (i) a fixed green background (triangles, Fig. 5), or (ii) a fixed red one (squares), the action spectra changed in a way that indicated greater prominence of (i) the 680 nm system (ii) the 540 nm green system that was not conspicuous without adaptation to red.4. These observations (on the tench Tinca) are contrary to the conclusions of Svaetichin & McNichol (on Gerridae) that the action spectrum is unaltered in shape by adaptation to coloured lights. The contribution of the green cones, for example, was actually absolutely greater under deep red adaptation.5. It is concluded that L-units receive signals from 680, 620, 540 nm and possibly also the blue cones, that the quantum catch in all these contribute to the hyperpolarization produced, but their interaction is more complicated than the simple addition of independent cone effects.

SUMMARY1. S-potentials from Luminosity-units in the excised eye of the tench (Tinca) were excited by white lights of various intensities and spatial distributions.2. When a small light spot of fixed size and intensity was presented at various distances from the recording electrode, the S-potential was found to suffer an exponential attenuation with distance ( Fig. 3

The Wiener theory of nonlinear system identification was applied to a three-stage neuron chain in the catfish retina in order to determine the functional relationship between the artificial polarization of the horizontal cell membrane potential and the resulting discharge of the ganglion cell. A mathematical model was obtained that can predict quantitatively, with reasonable accuracy, the nonlinear, dynamic behavior of the neuron chain. The applicability of the method is discussed. We conclude that this is a very powerful method in the analysis of information transfer in the central nervous system.

Electrical properties of the muscle fiber membrane were studied in the barnacle, Balanus nubilus Darw. by using intracellular electrode techniques. A depolarization of the membrane does not usually produce an all-ornone spike potential in the normal muscle fiber even though a mechanical response is elicited. The intracellular injection of Ca++-binding agents (K 2 SO4 and K salt of EDTA solution, Ks citrate solution, etc.) renders the fiber capable of initiating all-or-none spikes. The overshoot of such a spike potential increases with increasing external Ca concentration, the increment for a tenfold increase in Ca concentration being about 29 my. The threshold membrane potential for the spike and also for the K conductance increase shifts to more positive membrane potentials with increasing [Ca++],ut. The removal of Na ions from the external medium does not change the configuration of the spike potential. In the absence of Ca++ in the external medium, the spike potential is restored by Ba++ and Sr++ but not by Mg++. The overshoot of the spike potential increases with increasing [Ba++]out or [Sr++],,t. The Ca influx through the membrane of the fiber treated with K 2 SO 4 and EDTA was examined with Ca 45 . The influx was 14 pmol per sec. per cm 2 for the resting membrane and 35 to 85 pmol per cm 2 for one spike. From these results it is concluded that the spike potential of the barnacle muscle fiber results from the permeability increase of the membrane to Ca++ (Ba++ or Sr++).