THE KINETICS OF PENETRATION : I. EQUATIONS FOR THE ENTRANCE OF ELECTROLYTES

When the only solute present is a weak acid, HA, which penetrates as molecules only into a living cell according to a curve of the first order and eventually reaches a true equilibrium we may regard the rate of increase of molecules inside as See PDF for Equation where P_M is the permeability of the protoplasm to molecules, M_o, denotes the external and M_i the internal concentration of molecules, A_i denotes the internal concentration of the anion A^- and See PDF for Equation (It is assumed that the activity coefficients equal 1.) Putting P_MF_M = V_M, the apparent velocity constant of the process, we have See PDF for Equation where e denotes the concentration at equilibrium. Then See PDF for Equation where t is time. The corresponding equation when ions alone enter is See PDF for Equation. where K is the dissociation constant of HA, P_A is the permeability of the protoplasm to the ion pair H⁺ + A^-, and A_ie denotes the internal concentration of A_i at equilibrium. Putting P_AKF_M = V_A, the apparent velocity constant of the process, we have See PDF for Equation and See PDF for Equation When both ions and molecules of HA enter together we have See PDF for Equation where S_i = M_i + A_i and S_ie is the value of S_i at equilibrium. Then See PDF for Equation V_M, V_A, and V_MA depend on F_M and hence on the internal pH value but are independent of the external pH value except as it affects the internal pH value. When the ion pair Na⁺ + A^- penetrates and Na_i = BA_i, we have See PDF for Equation and See PDF for Equation where P _NaA is the permeability of the protoplasm to the ion pair Na⁺ + A^-, Na_o and Na_i are the external and internal concentrations of Na⁺, See PDF for Equation, and V _Na is the apparent velocity constant of the process. Equations are also given for the penetration of: (1) molecules of HA and the ion pair Na⁺ + A^-, (2) the ion pairs H⁺ + A^- and Na⁺ + A^-, (3) molecules of HA and the ion pairs Na⁺ + A^- and H⁺ + A^-. (4) The penetration of molecules of HA together with those of a weak base ZOH. (5) Exchange of ions of the same sign. When a weak electrolyte HA is the only solute present we cannot decide whether molecules alone or molecules and ions enter by comparing the velocity constants at different pH values, since in both cases they will behave alike, remaining constant if F_M is constant and falling off with increase of external pH value if F_M falls off. But if a salt (e.g., NaA) is the only substance penetrating the velocity constant will increase with increase of external pH value: if molecules of HA and the ions of a salt NaA. penetrate together the velocity constant may increase or decrease while the internal pH value rises. The initial rate See PDF for Equation (i.e., the rate when M_i = 0 and A_i = 0) falls off with increase of external pH value if HA alone is present and penetrates as molecules or as ions (or in both forms). But if a salt (e.g., NaA) penetrates the initial rate may in some cases decrease and then increase as the external pH value increases. At equilibrium the value of M_i equals that of M_o (no matter whether molecules alone penetrate, or ions alone, or both together). If the total external concentration (S_o = M_o + A_o) be kept constant a decrease in the external pH value will increase the value of M_o and make a corresponding increase in the rate of entrance and in the value at equilibrium no matter whether molecules alone penetrate, or ions alone, or both together. What is here said of weak acids holds with suitable modifications for weak bases and for amphoteric electrolytes and may also be applied to strong electrolytes.     

COMPARATIVE STUDIES ON RESPIRATION : XXIV. THE EFFECTS OF CHLOROFORM ON THE RESPIRATION OF DEAD AND OF LIVING TISSUE.

1. Chloroform in low concentration (0.25 per cent) causes an increase in the rate of production of CO₂ in Ulva; this is followed by a decrease. In higher concentration (0.5 per cent) only a decrease is observed. 2. Assuming that the normal oxidation depends on the action of peroxide and peroxidase, experiments were made by placing Ulva in 1.0 per cent H₂O₂ and in Fe₂(SO₄)₃ (which acts like a peroxidase). The former diminishes the rate, the latter increases and subsequently decreases it. 3. When Ulva is killed in such a manner as to destroy the oxidizing enzymes, no CO₂ is produced unless H₂O₂ and Fe₂(SO₄)₃ are present. If to this mixture chloroform is added, the effect depends on the concentration of the iron. If the concentration is low there is an increase in the production of CO₂ followed by a decrease. If the concentration is high the rate appears to decrease from the start.     

CHEMICAL ANTAGONISM OF IONS : III. EFFECT OF SALT MIXTURES ON GELATIN ACTIVITY.

1.25 per cent gelatin solutions containing enough NaOH to bring them to pH 7.367 (or KOH to pH 7.203) were made up with various concentrations of NaCl, KCl and MgCl₂, alone and in mixtures, up to molar ionic strength. The effects of these salts on the pH were observed. MgCl₂ and NaCl alone lower the pH of the Na gelatinate or the K gelatinate, in all amounts of these salts. KCl first lowers the pH (up to 0.01 M K⁺), then raises the pH. Mixtures of NaCl and KCl (up to 0.09 M of the salt whose concentration is varied) raise the pH; then (up to 0.125 M Na⁺ or K⁺) lower the pH; and finally (above 0.125 M) behave like KCl alone. Mixtures of MgCl₂ and NaCl raise the pH up to 0.10 M Na⁺, and lower it up to 0.15 M Na⁺ regardless of the amount of MgCl ₂. Higher concentrations of NaCl have little effect, but the pH in this range of NaCl concentration is lowered with increase of MgCl₂. Mixtures of MgCl₂ and KCl behave as above described (for MgCl₂ and NaCl) and the addition of NaCl plus KCl to gelatin containing MgCl₂ produces essentially the same effect as the addition of either alone, except that the first two breaks in this curve come at 0.07 M and 0.08 M [Na⁺ + K⁺] and there is a third break at 0.12 M. In this pH range the free groups of the dicarboxylic acids and of lysine are essentially all ionized and the prearginine and histidine groups are essentially all non-ionized. The arginine group is about 84 per cent ionized. Hence we are studying a solution with two ionic species in equilibrium, one with the arginine group ionized, and one with it non-ionized. It is shown that the effect of each salt alone depends upon the effect of the cation on the activity of these two species due to combination. The anomalous effects of cation mixtures may be qualitatively accounted for if one or both of these species fail to combine with the cations in a mixture in proportion to the relative combination in solutions of each cation alone. Special precautions were taken to ensure accuracy in the pH measurements. The mother solutions gave identical readings to 0.001 pH and the readings with salts were discarded when not reproducible to 0.003 pH. All doubtful data were discarded.     

CHEMICAL ANTAGONISM OF IONS : IV. EFFECT OF SALT MIXTURES ON GLYCINE ACTIVITY.

The pH of a 0.01 molar solution of glycine, half neutralized with NaOH, is 9.685. Addition of only one of the salts NaCl, KCl, MgCl₂, or CaCl₂ will lower the pH of the solution (at least up to 1 µ). If a given amount of KCl is added to a glycine solution, the subsequent addition of increasing amounts of NaCl will first raise the pH (up to 0.007 M NaCl). Further addition of NaCl (up to 0.035 M NaCl) will lower the pH, and further additions slightly raise the pH. The same type of curve is obtained by adding NaCl to glycine solution containing MgCl₂ or CaCl₂ except that the first and second breaks occur at 0.015 M and 0.085 M NaCl, respectively. Addition of CaCl₂ to a glycine solution containing MgCl₂ gives the same phenomena with breaks at 0.005 M and 0.025 M CaCl; or at ionic strengths of 0.015 µCaCl₂ and 0.075 µCaCl₂. This indicates that the effect is a function of the ionic strength of the added salt. These effects are sharp and unmistakable. They are almost identical with the effects produced by the same salt mixtures on the pH of gelatin solutions. They are very suggestive of physiological antagonisms, and at the same time cannot be attributed to colloidal phenomena.     

CALCULATIONS OF BIOELECTRIC POTENTIALS : V. POTENTIALS IN HALICYSTIS

Interest in the study of Halicystis and of Valonia has been stimulated by discoveries of marked contrasts and striking similarities existing side by side. This is illustrated by new experiments with the alkali metals and alkaline earths. In Halicystis the apparent mobilities of K⁺, Rb⁺, Cs⁺, and Li⁺ (calculated by means of Henderson''s equation from changes in P.D. produced by replacing sea water by a mixture of equal parts of sea water and 0.6 M of various chlorides) are as follows, u _K, = 16, u _Rb = 16, u _Cs = 4.4, and u _Li = 0.2; u _Na is taken as 0.2. These values resemble those in Valonia except that in the latter u _Cs is about 0.2. No calculation is made for u _NHNH4, because in these experiments even at low pH so much NH₃ is present that the sign of the P.D. may reverse. This does not happen with Valonia. According to Blinks, NH₄ ⁺ at pH 5 in low concentrations acts like K⁺. The calculation gives u _Mg = 1.9 which is similar to the value found for Valonia. No calculation can be made for CaCl₂ since it produces protoplasmic alterations and in consequence Henderson''s equation does not apply. This differs from Valonia. Evidently these plants agree closely in some aspects of electrical behavior but differ widely in others.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : X. AN EXPERIMENTAL TEST OF SOME ASPECTS OF THE TEORELL AND MEYER-SIEVERS THEORIES OF ELECTRICAL MEMBRANE BEHAVIOR

1. The Teorell, Meyer-Sievers theory characterizes the electrochemical behavior of membranes by their selectivity constant "A_p" which is derived conventionally from concentration potential measurements at various concentration levels. The selectivity constant may, however, be derived also from entirely independent, different experimental data, namely base exchange studies. The constants arrived at in this second way are designated as "A_b." The selectivity constants derived by these two methods must be in reasonable, at least semiquantitative agreement if the basic assumptions of the theory are correct. 2. The selectivity constants A_p and A_b were determined for eleven different sets of membranes of different electrochemical activity and of different (8.2 to 80 volume per cent) water content. 3. The potentiometric selectivity constants A_p are in most cases several orders of magnitude greater than the corresponding A_b values. With membranes of great porosity and high electrochemical activity the A_b values approach at least in order of magnitude the A_p values. 4. It is concluded that the unexpectedly large discrepancy between the A_p and A_b values is due to some inherent weakness of the Teorell, Meyer-Sievers theory, most likely to its neglect of any structural factors.     

ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. X

The inheritance of elements of geotropic performance in lines of rats (A and B) has been investigated by examining the orientation of young offspring produced in matings of F_1(AxB) with A: Previous studies had shown that the three recognizable groups of receptor elements concerned in geotropic orientation in each of these lines appeared to be inherited in such a way that B groups were dominant with respect to A groups, although this was to a minor extent complicated by influences affecting the variation of orientation as well as the exact form of the curve relating orientation angle (θ) to slope of surface. In the backcross F₁ x A, therefore, at least eight different types of curves were to be expected. These are in fact identifiable among the forty-one individuals carefully studied. Their classification is concordant with the behavior of the respective indices of variation of θ, for which an interpretation has been provided. The basic result is, therefore, that the three receptor groups of excitation units are inherited independently, and alternatively as regards the members of a homologous pair, and that rather simple dominance relations obtain between homologous groups from the two races, namely that a B effect is dominant over the homologous A effect. This interpretation has been tested in various ways, and is in principle completely consistent with the results of a similar experiment involving races A and K.     

THE RHEOLOGY OF THE BLOOD. III

The authors have confirmed the fact that blood serum and plasma behave rheologically like a true viscous liquid. It is true for whole blood only to a first approximation, but with this reservation they have studied the available data and extended the equation of Bingham and Durham to cover protein solutions of various concentrations and at various temperatures as well as mixtures of proteins and corpuscles present in whole blood. If Φ is the fluidity of whole blood, Φ₁ is the fluidity of water and ΔΦ = Φ – Φ₁, then ΔΦ = β₁ b ₁ + β₂ b ₂ + β₃ b ₃ + ··· where β₁, β₂, β₃, etc., are constants for the fluidity lowering of the salts, albumin, globulin, fibrinogen, and the corpuscles, etc., present in the whole blood. The conclusions from the data referred to are intended to buttress this simple equation (6).     

DYNAMICS OF NERVE CELLS : I. THE TEMPERATURE COEFFICIENT OF THE NEUROGENIC RHYTHM OF THE HEART OF LIMULUS POLYPHEMUS.

In the case of the heart of Limulus polyphemus the same magnitude and variation of the temperature coefficient (Q ₁₀) is obtained from the whole heart as from the ganglion alone. From the magnitude of the temperature coefficients and their variation with changes of temperature we may conclude that the rate of the heart beat is determined by alteration of chemical processes in the ganglion cells.     

Photosynthesis in Grass Species Differing in Carbon Dioxide Fixation Pathways: III. OXYGEN RESPONSE AND ENZYME ACTIVITIES OF SPECIES IN THE LAXA GROUP OF PANICUM

Measurements of CO₂ exchange at varying O₂ concentrations in seven grass species of the Laxa group of Panicum and activities of five photosynthetic enzymes were compared to values obtained for these characters in a cool season C₃ grass, tall fescue (Festuca arundinacea Schreb.) and a C₄ grass, P. maximum Jacq. Plants were divided into three groups on the basis of the inhibition of apparent photosynthesis by 21% O_2. Rates of apparent photosynthesis in P. prionitis Griseb. and P. maximum were virtually unaffected by changes in O₂ concentration. In another group consisting of P. hylaeicum Mez., P. rivulare Trin., P. laxum Sw., and tall fescue apparent photosynthesis was inhibited by 28.2 to 36.0% at 21% O_2. An intermediate inhibition of 20.6 to 23.3% at 21% O₂ was exhibited by P. milioides Nees ex Trin., P. schenckii Hack., and P. decipiens Nees ex Trin. The CO₂ compensation concentration for P. prionitis and P. maximum was low (≤6 microliters per liter CO₂ at 21% O₂) and affected little by O₂, whereas values for P. hylaeicum, P. rivulare, P. laxum, and tall fescue were much greater, and increased almost linearly from 2 to 48% O_2. Values for P. milioides, P. schenckii, and P. decipiens were intermediate to the other two groups. The effect of O₂ on total leaf conductance to CO₂ was similar to the C₃ grasses and the intermediate Panicums. However, estimates of photorespiration in the intermediate species were low and changed little with O₂ in comparison to estimates for the C₃ species which were higher and increased greatly with increased O_2.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : X. MODIFICATIONS OF THE FLICKER RESPONSE CONTOUR,AND THE SIGNIFICANCE OF THE AVIAN PECTEN

1. When there is projected on the retina (man, monocularly) the shadow of a grid which forms a visual field in several distinct pieces (not including the fovea in the present tests), the ordinary properties of the flicker recognition contour (F vs. log I) as a function of the light-time cycle fraction (t_L) can be markedly disturbed. In the present experiments flicker was produced by the rotation of a cylinder with opaque vertical stripes. In the absence of such a grid shadow the "cone" segments of the contours form a set in which F_max. and the abscissa of inflection are opposite but rectilinear functions of t_L, while the third parameter of the probability integral (σ''_{log I}) remains constant. This is the case also with diverse other animals tested. In the data with the grid, however, analysis shows that even for low values of t_L (up to 0.50) there occurs an enhancement of the production of elements of neural effect, so that F_max. rises rather than falls as ordinarily with increase of t_L, although σ''_{log I} stays constant and hence the total number of acting units is presumed not to change. This constitutes valid evidence for neural integration of effects due to the illumination of separated retinal patches. Beginning at t_L = 0.75, and at 0.90, the slope of the "cone" curve is sharply increased, and the maximum F is far above its position in the absence of the grid. The decrease of σ''_{log I} (the slope constant) signifies, in terms of other information, an increase in the number of acting cone units. The abscissa of inflection is also much lowered, relatively, whereas without the grid it increases as t_L is made larger. These effects correspond subjectively to the fact that at the end-point flicker is most pronounced, on the "cone" curve, along the edges of the grid shadow where contrast is particularly evident with the longer light-times. The "rod" portion of the F - log I contour is not specifically affected by the presence of the grid shadow. Its form is obtainable at t_L = 0.90 free from the influence of summating "cone" contributions, because then almost no overlapping occurs. Analysis shows that when overlapping does occur a certain number of rod units are inhibited by concurrent cone excitation, and that the mean contribution of elements of neural action from each of the non-inhibited units is also reduced to an extent depending on the degree of overlap. The isolated "rod" curve at t_L = 0.90 is quite accurately in the form of a probability integral. The data thus give a new experimental proof of the occurrence of two distinct but interlocking populations of visual effects, and experimentally justify the analytical procedures which have been used to separate them. 2. The changing form of the F - log I contour as a function of t_L, produced in man when the illuminated field is divided into parts by a shadow pattern, is normally found with the bird Taeniopygia castenotis (Gould), the zebra finch. The retina has elements of one general structural type (cones), and the F - log I contour is a simplex symmetrical probability integral. The eye of this bird has a large, complex, and darkly pigmented pecten, which casts a foliated shadow on the retina. The change in form of the F - log I curve occurs with t_L above 0,50, and at t_L = 0.90 is quite extreme. It is more pronounced than the one that is secured in the human data with the particular grid we have used, but there is no doubt that it could be mimicked completely by the use of other grids. The increase of flicker acuity due to the pecten shadow is considerable, when the dark spaces are brief relative to the light. The evidence thus confirms the suggestion (Menner) drawn from comparative natural history that the visual significance of the avian pecten might be to increase the sensory effect of small moving images. It is theoretically important that (as in the human experiment) this may be brought about by an actual decrease of effective retinal area illuminated. It is also significant theoretically that despite the presence of shadows of pecten or of grid, and of the sensory influences thus introduced, the probability integral formulation remains effective.     

THE KINETICS OF PENETRATION : VI. SOME FACTORS AFFECTING PENETRATION

Some of the factors affecting penetration in living cells may be advantageously studied in models in which the organic salts KG and NaG diffuse from an aqueous solution A, through a non-aqueous layer B (representing the protoplasmic surface) into an aqueous solution C (representing the sap and hence called artificial sap) where they react with CO₂ to form KHCO₃ and NaHCO₃. Their relative proportions in C depend chiefly on the partition coefficients and on the diffusion constants in the non-aqueous layer. But the ratio is also affected by other variables, among which are the following: 1. Temperature, affecting diffusion constants and partition coefficients and altering the thickness of the unstirred layers by changing viscosity. 2. Viscosity (especially in the non-aqueous layers) which depends on temperature and the presence of solutes. 3. Rate of stirring, which affects the thickness of the unstirred layers and the transport of electrolyte in those that are stirred. 4. Shape and surface area of the non-aqueous layer. 5. Surface forces. 6. Reactions occurring at the outer surface such as loss of water by the electrolyte or its molecular association in the non-aqueous phase. The reverse processes will occur at the inner surface and here also combinations with acids or other substances in the "artificial sap" may occur. 7. Outward diffusion from the artificial sap. The outward movement of KHCO₃ and NaHCO₃ is small compared with the inward movement of KG and NaG when the concentrations are equal. This is because the partition coefficients³ of the bicarbonates are very low as compared with those of NaG and KG. Since CO₂ and HCO₃ ^- diffuse into A and combine with KG and NaG the inward movement of potassium and sodium falls off in proportion as the concentration of KG and NaG is lessened. 8. Movement of water into the non-aqueous phase and into the artificial sap. This may have a higher temperature coefficient than the penetration of electrolytes. 9. Variation of the partition coefficients with concentration and pH. Many of these variables may occur in living cells. (It happens that the range of variation in the ratio of potassium to sodium in the models resembles that found in Valonia.)     

STUDIES ON THE METABOLISM OF AUTOTROPHIC BACTERIA : II. THE NATURE OF THE CHEMOSYNTHETIC REACTION

In a study of chemosynthesis (the fixation of CO₂ by autotrophic bacteria in the dark) in Thiobacillus thiooxidans, the data obtained support the following conclusions: 1. CO₂ can be fixed by "resting cells" of Thiobacillus thiooxidans; the fixation is not "growth bound." 2. The physiological condition of the cell is of considerable importance in determining CO₂ fixation. 3. CO₂ fixation can occur in the absence of oxidizable sulfur in "young" cells. The extent of this fixation appears to be dependent upon the pCO₂. 4. CO₂ fixation can also occur under anaerobic conditions and the presence of sulfur does not influence such fixation. 5. However, in the CO₂ fixation by cells in the absence of sulfur, only a limited amount of CO₂ can be fixed. This amount is approximately 40 µl. CO₂ per 100 micrograms bacterial nitrogen. After a culture has utilized this amount of CO₂ it no longer has the ability to fix CO₂ but releases it during its respiration. 6. Relatively short periods of sulfur oxidation can restore the ability of cells to fix CO₂ under conditions where sulfur oxidation is prevented. 7. It is possible to oxidize sulfur in the absence of CO₂ and to store the energy thus formed within the cell. It is then possible to use this energy at a later time for the fixation of CO₂ in the entire absence of sulfur oxidation. 8. Cultures of Thiobacillus thiooxidans respiring on sulfur utilize CO₂ in a reaction which proceeds to a zero concentration of CO₂ in the atmosphere. 9. CO₂ may act as an oxidizing agent for sulfur. 10. Hydrogen is not utilized by the organism. 11. It is possible to selectively inhibit sulfur oxidation and CO₂ fixation.     

ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. IX

Adult hybrid rats from the cross of races A x B show a total capacity to vary their geotropic performance which is identical with that of their B parents. The proportionate modifiable variability of geotropic orientation also agrees quantitatively with that for the B parents. These relationships are not disturbed by the action of adrenin, which leads to a distortion of the θ vs. α curve. Young rats of the F ₁ generation show a greater proportion of unmodifiable variation of geotropic orientation. It is pointed out that the present findings support the conclusion that the capacity of rats to exhibit variation of geotropic orientation is limited by their genetically determined composition and that the special condition in the young hybrids may be understood as due to a kind of temporary disharmony of developmental events.     

THE EFFECT OF RADIOACTIVE RADIATIONS AND X-RAYS ON ENZYMES : III. A UNIT OF MEASURE OF ACTIVITY FOR RADIUM EMANATION.

In this communication we have introduced a unit to express activity or power of a given preparation of radium emanation. We have named this unit the curie-power and defined it as the activity of 1 curie of radium emanation and its radioactive products in equilibrium with it. We suggest the introduction of this unit in order that we may make a more comprehensive statement of our experimental observation. In the radiochemical reaction effected by the radiations (beta and gamma) from radium emanation in which enzymes are inactivated the chemical change in a given system is a function of the product of two variables; namely, the average activity of the radium emanation, P_a, expressed in terms of the unit millicurie-power, and time, t, expressed in hours. This product has the dimensions of energy and is identical with W which is measured in terms of the energy unit, millicurie-power hours.     

A THEORY OF INJURY AND RECOVERY : II. EXPERIMENTS WITH MIXTURES.

1. The equations which serve to predict the injury of tissue in 0.52 M NaCl and in 0.278 M CaCl₂ and its subsequent recovery (when it is replaced in sea water) also enable us to predict the behavior of tissue in mixtures of these solutions, as well as its recovery in sea water after exposure to mixtures. 2. The reactions which are assumed in order to account for the behavior of the tissue proceed as if they were inhibited by a salt compound formed by the union of NaCl and CaCl₂ with some constituent of the protoplasm (certain of these reactions are accelerated by CaCl₂). 3. In this and preceding papers a quantitative theory is developed in order to explain: (a) the toxicity of NaCl and CaCl₂; (b) the antagonism between these substances; (c) the fact that recovery (in sea water) may be partial or complete, depending on the length of exposure to the toxic solution.     

CALCULATIONS OF BIOELECTRIC POTENTIALS : IV. SOME EFFECTS OF CALCIUM ON POTENTIALS IN NITELLA

In Nitella the substitution of KCl for NaCl changes the P.D. in a negative direction. In some cases this change is lessened by adding solid CaCl₂ to the solution of KCl. This may be due to lessening the partition coefficient of KCl or to decreasing the solubility of an organic substance which sensitizes the cell to the action of KCl. Little or no correlation exists between this effect of calcium and its ordinary antagonistic action in producing a balanced solution which preserves the life of the cell indefinitely. CaCl₂ is negative to NaCl but positive to KCl. The effects of mixtures of KCl, NaCl, and CaCl₂ are discussed. The concentration effect of a mixture of KCl + CaCl₂ shows certain peculiarities due to action currents: these resemble those found with pure KCl. These studies and others on Nitella, Valonia, and Halicystis indicate that mobilities and partition coefficients are variable and can be brought under experimental control.     

THE EFFECTS OF RADIATIONS ON BIOLOGICAL SYSTEMS : II. IMMEDIATE AND SUBSEQUENT EFFECTS OF X-RAY IRRADIATION UPON RESPIRATION OF DROSOPHILA LARVAE

By means of measurement of CO₂ respiratory rates it has been possible to observe immediate and latent effects of x-ray irradiations upon Drosophila larvae. The observations were extended over a period of several days, the duration of the prepupal period being observed also. In every instance a significant decrease in the rate of CO₂ respiration was observed immediately after irradiation. This decrease was univariant with the period of irradiation within the experimental limits.     

THEORY AND MEASUREMENT OF VISUAL MECHANISMS : III. ΔI AS A FUNCTION OF AREA,INTENSITY, AND WAVE-LENGTH,FOR MONOCULAR AND BINOCULAR STIMULATION

Measurements of ΔI as a function of retinal area illuminated have been obtained at various levels of standard intensity I ₁, using "white" light and light of three modal wave-lengths (λ465, 525, 680), for monocular stimulation and for simultaneous excitation of the two eyes ("binocular"), using several methods of varying (rectangular) area and retinal location, with control of exposure time. For data homogeneous with respect to method of presentation, log ΔI_m = -Z log A + C, where ΔI = Ĩ ₂ – I ₁, A is area illuminated, and C is a terminal constant (= log ΔI_m for A = 1 unit) depending on the units in which ΔI and A are expressed, and upon I ₁. The equation is readily deduced on dimensional grounds, without reference to specific theories of the nature of ΔI or of retinal area in terms of its excitable units. Z is independent of the units of I and A. Experimentally it is found to be the same for monocular and binocular excitations, as is to be expected. Also as is expected it is not independent of λ, and it is markedly influenced by the scheme according to which A is varied; it depends directly upon the rate at which potentially excitable elements are added when A is made to increase. For simultaneous excitation of the two eyes (when of very nearly equivalent excitability), ΔĪ_B is less than for stimulation of either eye alone, at all levels of I ₁, A, λ. The mean ratio (ΔĪ_L + ΔĪ_R)/2 to ΔI^B was 1.38. For white light, doubling A on one retina reduces ΔI_m in the ratio 1.21, or a little less than for binocular presentation under the same conditions. These facts are consistent with the view that the properties of ΔI are quantitatively determined by events central to the retina. The measure σ_1ΔI of organic variation in discrimination of intensities and ΔI_m are found to be in simple proportion, independent of I ₁, A, λ (and exposure time). Variability (σ_1ΔI) is not a function of the mode of presentation, save that it may be slightly higher when both retinas are excited, and its magnitude (for a given level of ΔI_m) is independent of the law according to which the adjustable intensity I ₂ is instrumentally controlled.