THE PHOTOCHEMICAL NATURE OF THE PHOTOSENSORY PROCESS

On page 243, Vol. ii, No. 3, January 20, 1920, line 12 (counting each equation as a line) for a photochemical reaction read a reversible photochemical reaction.     

THE INFLUENCE OF TEMPERATURE ON THE PHOTOSENSORY LATENT PERIOD

1. The effect of temperature on the photosensory latent period in Pholas dactylus is accurately described by the Arrhenius equation when µ = 18,300. 2. The adequacy of this equation has already been found for two other photosensitive animals, Mya and Ciona, which are very similar in behavior to Pholas. The value of µ is different for each of the three species studied. 3. This is taken to mean that though the organization of the receptor process is the same for the three species, the chemical materials concerned are very likely different.     

THE PHOTOCHEMICAL BASIS OF ANIMAL HELIOTROPISM

1. Experiments on the heliotropic orientation of Limulus were made which confirmed Loeb''s photochemical theory of animal heliotropism proposed first in 1888 and 1889 in experiments on insects, and later in experiments on other forms of animals. 2. It is shown that these animals are oriented by light in such a way that the product I x t x cos α is the same for the symmetrical photosensitive elements of the eyes or the skin, where I is the intensity of the light, t the duration of illumination, and α the angle of incidence of the light at the surface element of the photosensitive organ. 3. When this equation holds, the products of decomposition by light must be the same in symmetrical elements of the eyes or skin, and the influence of these products of decomposition on the tension of symmetrical muscles of the locomotor organs of the animal must be the same. As a consequence the animal must move in the path of light, either to or from the source of light.     

THE RELATION OF TIME,INTENSITY AND WAVE-LENGTH IN THE PHOTOSENSORY SYSTEM OF PHOLAS

The most effective point in the visible spectrum for the stimulation of Pholas is 550 mµ. On the red side, the effectiveness drops rapidly to almost zero. On the violet side, the effectiveness drops to about half, and rises again in such a way as to indicate a possible second maximum in the near ultra-violet. On the basis of certain ideas these data are assumed to represent the properties of the absorption spectrum of the photosensitive system in Pholas. A comparison with Mya shows that the absorption spectra of the photosensitive systems in the animals are distinctly different. Nevertheless the way in which intensity and reaction time are related in the two animals are found to be identical. The conclusion is then drawn from this and from previous work, that although the fundamental properties of the photoreceptor process show an identical organization in several different animals, the materials which compose these processes are specific.     

A NOTE ON THE RELATIVE PHOTOSENSORY EFFECT OF POLARIZED LIGHT

Experiments were made to compare the stimulating effectiveness of vertically and horizontally polarized lights and non-polarized lights of equal intensity upon phototropic movements of the beetle Tetraopes tetraopthalmus; and to compare the effectiveness of two light beams polarized at right angles to one another upon phototropic orientation of the land isopod Cylisticus convexus. Tetraopes is positively, and Cylisticus, negatively phototropic. Tests were also made of the intensities of horizontally and of vertically polarized light required to inhibit stereotropism in larvæ of Tenebrio. Under the conditions of the tests, no certain qualitative effect connected with polarization could be detected.