Theory of Light Sensations.

(P. Lasareff—Action des substances vasodilatatrices sur la sensibilité de l’oeil au cours de la vision périphérique and P. Lasareff—théorie des sensations lumineuses pendant la vision centrale avec des éclairages de la rétine de courte durée, Archives des Sciences physiques 1918 I).

Lazarev’s works on questions of excitation, begun as early as 1904, set themselves a quite definite aim—to apply physicochemical methods of investigation to physiological problems.

There is no doubt that, as they develop, all the so-called exact sciences must pass over to the establishment of quantitative relations and laws. In the field of biology and physiology, a considerable factual material has already accumulated, making it possible to begin this necessary work of revealing quantitative connections. And only the familiar, and historically quite understandable, inertia of higher education—which has not given natural scientists and physicians the necessary skill in handling the physico-mathematical apparatus—not only renders them helpless in applying physicochemical methods, but often even leaves them in complete ignorance of the existence of such methods.

The articles named in the title represent the further development of those ideas which were given in the author’s doctoral dissertation, “Fading of Dyes and Pigments in the Visible Spectrum,” and in his “Investigations on the Ionic Theory of Excitation.” After these works, rich in factual and theoretical material, the picture of the excitation of visual sensation—this primary stage of the visual act—appears quite definite, consisting of a combination of a photochemical reaction and a process of removal of the decomposition products.

The further task—to give a theory of the propagation of the nervous process—appears at the present time to be unresolved, since the high velocities make explanation of this phenomenon by diffusion doubtful. True, the works of Srebnitsky and Mintz (not yet published), carried out in Lazarev’s laboratory, and the work of Meinecke in Luther’s laboratory, indicate the possibility of an extraordinary increase in velocities under catalysis and a decrease in the diameter of those vessels in which the reaction takes place.

In the first of the articles named in the title, the influence of amyl nitrite on the sensitivity of the eye is considered. In the equation of the visual act

\[ \frac{dc'_1}{dt}=a_1 kIC-a_2 C'_1 \]

the second term of the right-hand side characterizes the process of removal of decomposition products, and \(\alpha_2\) must vary with the conditions of blood circulation. The coefficient \(\alpha_2\) enters into the equation relating the intensity of illumination \(I\) to the time \(t\) for the threshold of irritation.

\[ I=\frac{B}{C\alpha_1 k\left(1-\frac{B}{2c}\right)\cdot t} +\frac{B\alpha_2}{2C\alpha_1 k\left(1-\frac{B}{2c}\right)} . \]

For constant \(t\), the coefficient \(\alpha_2\) is linearly related to \(I\). From an increase in \(I\) we may judge an increase in \(\alpha_2\).

The measurements performed did indeed yield this increase.

The second article placed in the title concerns deviations from the law established by Lazarev and given in the first article,

\[ I.t=a+bt \]

The observations of Broca and Sulzer showed that, when the eye is illuminated, the sensation of brightness at first increases with increasing \(t\), and then falls. Lazarev makes the hypothesis that, in the decomposition of the retinal pigment, substances are obtained that cause the formation of substances \(B\) that irritate the nerve endings; in their turn the substances \(B\) pass into substances \(D\), which do not cause irritation. It turns out that the integral of the differential equation formulated under this assumption is

\[ I=A\left(e^{-\omega t}-e^{-\omega_1 t}\right) \]

and expresses quite satisfactorily the results of the experimental investigation.

It is interesting to note that the same relation between irritation and the time of the irritation threshold was found by V. Henri under the action of ultraviolet rays on a small animal of the crustacean species Cyclops.

B. V. Ilyin.