THE KINETICS OF OSMOTIC SWELLING IN LIVING CELLS

The rate of swelling of unfertilized sea urchin eggs in hypotonic sea water was investigated. Analysis of curves leads to the following conclusions. 1. The rate of swelling follows the equation, See PDF for Equation where V _eq., V ₀, and V_t stand for volume at equilibrium, at first instant, and at time t, respectively, the other symbols having their usual significance. This equation is found to hold over a wide range of temperatures and osmotic pressures. This relation is the one expected in a diffusion process. 2. The rate of swelling is found to have a high temperature coefficient (Q ₁₀ = 2 to 3, or µ = 13,000 to 19,000). This deviation from the usual effect of temperature on diffusion processes is thought to be associated with changes in cell permeability to water. The possible influence of changes in viscosity is discussed. 3. The lower the osmotic pressure of the solution, the longer it takes for swelling of the cell. Thus at 15° in 80 per cent sea water, the velocity constant has a value of 0.072, in 20 per cent sea water, of 0.006.     

THE EFFECT OF TEMPERATURE ON THE MECHANICAL ACTIVITY OF THE GILLS OF THE OYSTER (OSTREA VIRGINICA Gm.)

1. The method is described whereby the rate of flow produced by the gills of the oyster can be measured accurately. 2. The rate of doing work in maintaining a constant current along the glass tube can be expressed by the formula W = 2πlµ S ², where W = ergs/sec., l = length of the tube, µ = viscosity in poises, and S = speed at the axis of the tube. 3. The relationship between the rate of doing work and the temperature cannot be described by the equation of Arrhenius. 4. The optimum temperature for the mechanical activity of the gills lies between 25° and 30°C. Below 5° no current is produced, though the cilia are beating. Ciliary motion stops entirely at the freezing temperature of sea water. 5. The factors responsible for the production of current are discussed. The study of the relations between the variability of the rate of flow and the temperature shows that between 15° and 25°C. the absolute variability remains constant and increases considerably above 25° and below 15°. The rôle of the coordination in the production of current is discussed, and the conclusion is reached that coordination is affected by the changes in temperature.     

SYNERESIS AND SWELLING OF GELATIN

1. When solid blocks of isoelectric gelatin are placed in cold distilled water or dilute buffer of pH 4.7, only those of a gelatin content of more than 10 per cent swell, while those of a lower gelatin content not only do not swell but actually lose water. 2. The final quantity of water lost by blocks of dilute gelatin is the same whether the block is immersed in a large volume of water or whether syneresis has been initiated in the gel through mechanical forces such as shaking, pressure, etc., even in the absence of any outside liquid, thus showing that syneresis is identical with the process of negative swelling of dilute gels when placed in cold water, and may be used as a convenient term for it. 3. Acid- or alkali-containing gels give rise to greater syneresis than isoelectric gels, after the acid or alkali has been removed by dialysis. 4. Salt-containing gels show greater syneresis than salt-free gels of the same pH, after the salt has been washed away. 5. The acid and alkali and also the salt effect on syneresis of gels disappears at a gelatin concentration above 8 per cent. 6. The striking similarity in the behavior of gels with respect to syneresis and of gelatin solutions with respect to viscosity suggests the probability that both are due to the same mechanism, namely the mechanism of hydration of the micellæ in gelatin by means of osmosis as brought about either by diffusible ions, as in the presence of acid or alkali, or by the soluble gelatin present in the micellæ. The greater the pressures that caused swelling of the micellæ while the gelatin was in the sol state, the greater is the loss of water from the gels when the pressures are removed. 7. A quantitative study of the loss of water by dilute gels of various gelatin content shows that the same laws which have been found by Northrop to hold for the swelling of gels of high concentrations apply also to the process of losing water by dilute gels, i.e. to the process of syneresis. The general behavior is well represented by the equations: See PDF for Equation and See PDF for Equation where P ₁ = osmotic pressure of the soluble gelatin in the gel, P ₂ = stress on the micellæ in the gelatin solution before setting, K_e = bulk modulus of elasticity, V_o = volume of water per gram of dry gelatin at setting and V_e = volume of water per gram of gelatin at equilibrium.     

TEMPERATURE AND FORWARD MOVEMENT OF PARAMECIUM

1. The rate of forward movement in Paramecium as affected by changes in temperature can be described accurately in terms of the Arrhenius equation. See PDF for Equation 2. For the range from 6–15°, µ = 16,000; from 16–40°, µ = 8,000. These values fall within the limits characteristic for chemical processes. 3. On the principle of velocity control by the slowest rate, it is assumed that in Paramecium at temperatures above normal, control passes from one underlying reaction to another. 4. The views expressed by Rice, the recent results of Crozier, and certain µ values given by Arrhenius all suggest that µ = 16,000 may represent an oxidation, and µ = 8,000 either a modified oxidation or an hydrolysis. 5. For the system of controls, the catenary series O → A → E with the lower µ value attached to the precursor reaction is adequate. We may also assume a cyclical system analogous to Meyerhof''s conception of carbohydrate metabolism in muscle. In this case it is necessary to assign µ = 16,000 to the oxidation of A and E and µ = 8,000 to the synthesis E → O. This model also accounts for the fact that the data might be interpreted as involving, apparently, a depletion of A at the higher temperature.     

DIRECT COUNTING AND SIZING OF MITOCHONDRIA IN SOLUTION

Resistive particle counting has been developed for the accurate sizing and counting of mitochondria in solution. The normal detection limit with a 30 µ aperture is 0.48 µ diameter, or 0.056 µ³ particle volume The mean volume of rat liver mitochondria was 0.42 µ³ or 0.93 µ in diameter. The average value for numbers of particles per milligram of mitochondrial protein was 4.3 x 10³, and per gram of rat liver was about 11 x 10¹⁰. These values compare satisfactorily with those derived by light microscopy and electron microscopy. The mean volume for mitochondria from rat heart was 0 60 µ³ and from rat kidney cortex, 0.23 µ³. These values agree within 15% of those determined by electron microscopy of whole tissue. Mitochondrial fragility and contaminating subcellular organelles were shown to have little influence on the experimentally determined size distributions The technique may be applied to rapid swelling studies, as well as to estimations of the number and size of mitochondria from animals under different conditions such as liver regeneration and hormonal, pathological, or drug-induced states Mitochondrial DNA, RNA, cytochrome c-oxidase, cytochrome (a ÷ a₃), and iron were nearly constant per particle over large differences in particle size. Such data may be particularly valuable for biogenesis studies and support the hypothesis that the net amount per particle of certain mitochondrial constituents remains constant during mitochondrial growth and enlargement     

Determination of Equivalent Pore Radius for Human Red Cells by Osmotic Pressure Measurement

A new method has been developed to measure the equivalent pore radius in cellular membranes, and has been applied to human red cells. When red cells are suddenly introduced into a non-isosmolar concentration of non-lipid-soluble non-electrolyte molecules, water will enter or leave the cell. The rate of cell swelling or shrinking is determined and extrapolated to zero time to give the initial rate of volume change. By suitable adjustment of the concentration of the external solution the initial rate may be brought to zero. The transient equilibrium concentration, determined by interpolation from experimental data, gives a measure of Staverman's reflection coefficient, σ. The zero time method has enabled us to determine σ for nine permeant molecules. σ is directly related to the equivalent pore radius; the experimental data lead to a value of 4.2 Å for the equivalent pore radius in man, in good agreement with the previous figure of 3.5 Å given by Paganelli and Solomon. The zero time method offers a number of advantages over previous methods for determination of this parameter. It requires no measurement of the rate of water entrance into the cell, and is essentially independent of the kinetics of cell swelling. It may be applied to a variety of living cells so that many additional membranes may now be characterized in terms of their equivalent pore radius.     

STIMULATION OF FUNDULUS BY OXALIC AND MALONIC ACIDS AND BREATHING RHYTHM AS FUNCTIONS OF TEMPERATURE

1. Chemical stimulation as a function of temperature was studied by using oxalic acid in fresh and salt water and malonic acid in salt water as stimulating agents on Fundulus. According to the Arrhenius equation the following µ values were obtained for the various acid solutions between 0 and 29°C.: for 0.002N oxalic in fresh water—15,800; 33,000; for 0.0008N oxalic in fresh water—15,800; 33,000; 48,000; for 0.002N oxalic in salt water—19,400; 24,100; 56,500; for 0.004N and 0.002N malonic in salt water—20,600; 65,000. At a critical temperature there is a sharp transition from one thermal increment to another. 2. The chemical processes controlling stimulation do not change with concentration, for different normalities of a single acid yield the same µ values. Distinctly different temperature characteristics were obtained for stimulation by oxalic in salt and fresh water. Likewise stimulation by oxalic and malonic in salt water yielded very different increments. This temperature study indicates that the controlling chemical reactions determining rate of response are different for the same acid in two different environments, or for two dibasic acids in the same environment. Other work indicates, however, that the fundamental stimulation system is the same for all the adds in both environments. Chemical rather than physical processes limit the rate of response since all the values are above 15,000. Stimulation depends upon a series of interrelated chemical reactions, each with its own temperature characteristic. Under varying conditions (e.g. change of temperature, environment, or acid) different chemical reactions may become the slowest or controlling process which determines the rate of response. 3. The variation of response, as measured by the probable error of the mean response time of the fish, is the same function of temperature as reaction time itself. Hence variability is not independent of reaction time and is controlled by the same catenary series of events which determine rate of response to stimulation. 4. Breathing rhythm of Fundulus as related to temperature was studied in both salt and fresh water. In salt water the temperature characteristic is 8,400 while in fresh water it is 16,400 below 9.5°C., and 11,300 above this critical temperature. These µ values are typical of those which have been reported by other workers for respiratory and oxidative biological phenomena. A change in thermal increment with an alteration in environment indicates that different chemical reactions with characteristic velocity constants are controlling the breathing rhythm in salt and fresh water.     

THE RATE OF OXYGEN UTILIZATION BY YEAST AS RELATED TO TEMPERATURE

Suspensions of the yeast Saccharomyces cerevisiae gave reproducible rates of O₂ uptake over a period of 6 months. The relation of rate of consumption of O₂ to temperature was tested over a wide range of temperatures, and the constant in the formulation of the relationship is found to be reproducible. The values of this constant (µ) have been obtained for five separate series of experiments by three methods of estimation. The variability of µ has the following magnitudes: the average deviation of a single determination expressed as per cent of the mean is ±2 per cent in the range 30–15°, and ±0.8 per cent in the range 15–3°C. This constancy of metabolic activity measured as a function of temperature can then be utilized for more precise investigations of processes controlling the velocity of oxidations of substrates, and of respiratory systems controlled by intracellular respiratory pigments. The data plotted according to the Arrhemus equation give average values of the constant µ as follows: for the range 35–30°, µ = 8,290; 30–15°, µ = 12,440 ±290; 15–3°, µ = 19,530 ±154. The critical temperatures are at 29.0° and 15.7°C. A close similarity exists between these temperature characteristics (µ) and values in the series usually obtained for respiratory activities in other organisms. This fact supports the view that a common system of processes controls the velocities of physiological activities in yeast and in other organisms.     

THE EFFECT OF TEMPERATURE UPON FACET NUMBER IN THE BAR-EYED MUTANT OF DROSOPHILA : PART III.

Three strains of the bar-eyed mutant of Drosophila melanogaster Meig have been reared at constant temperatures over a range of 15–31°C. The mean facet number in the bar-eyed mutant varies inversely with the temperature at which the larvæ develop. The temperature coefficient (Q₁₀) is of the same order as that for chemical reactions. The facet-temperature relations may be plotted as an exponential curve for temperatures from 15–31°. The rate of development of the immature stages gives a straight line temperature curve between 15 and 29°. Beyond 29° the rate decreases again with a further rise in temperature. The facet curve may be readily superimposed on the development curve between 15 and 27°. The straight line feature of the development curve is probably due to the flattening out of an exponential curve by secondary factors. Since both the straight line and the exponential curve appear simultaneously in the same living material, it is impractical to locate the secondary factors in enzyme destruction, differences in viscosity, or in the physical state of colloids. Differential temperature coefficients for the various separate processes involved in development furnish the best basis for an explanation of the straight line feature of the curve representing the effect of temperature on the rate of physiological processes. Facet number in the full-eyed wild stock is not affected by temperature to a marked degree. The mean facet number for fifteen full-eyed females raised at 27° is 859.06. The mean facet number for the Low Selected Bar females at 27° is 55.13; for the Ultra-bar females at 27° it is 21.27. A consistent sexual difference appears in all the bar stocks, the females having fewer facets. This relation may be expressed by the sex coefficient, the average value of which is 0.791. The average observed difference in mean facet number for a difference of 1°C. in the environment in which the flies developed is 3.09 for the Ultra-bar stock and 14.01 for the Low Selected stock. The average proportional differences in the mean for a difference of 1°C. are 9.22 per cent for Ultra-bar, and 14.51 for Low Selected. The differences in the number of facets per °C. are greatest at the low and least at the high temperatures. The difference in the number of facets per °C. varies with the mean. The proportional differences in the mean per °C. are greatest at the lower (15–17.5°) and higher (29–31°) temperatures and least at the intermediate temperatures. Temperature is a factor in determining facet number only during a relatively short period in larval development. This effective period, at 27°, comes between the end of the 3rd and the end of the 4th day. At 15°, this period is initiated at the end of 8 days following a 1st day at 27°. At 27° this period is approximately 18 hours long. At 15° it is approximately 72 hours long. The number of facets and the length of the immature stage (egg-larval-pupal) appear related when the whole of development is passed at one temperature. That the number of facets is not dependent upon the length of the immature stage is shown by experiments in which only a part of development was passed at one temperature and the remainder at another. Temperature affects the reaction determining the number of facets in approximately the same way that it affects the other developmental reactions, hence the apparent correlation between facet number and the length of the immature stage. Variability as expressed by the coefficient of variability has a tendency to increase with temperature. Standard deviation, on the other hand, appears to decrease with rise in temperature. Neither inheritance nor induction effects are exhibited by this material. This study shows that environment may markedly affect the somatic expression of one Mendelian factor (bar eye), while it has no visible influence on another (white eye).     

THE SWELLING OF GELATIN AND THE VOLUME OF SURROUNDING SOLUTION

The swelling of isoelectric gelatin added to various volumes of acid of different concentration at 5°C. has been determined. The swelling is determined only by the concentration of the supernatant solution at equilibrium and is independent of the volume of acid. Similar experiments with unpurified gelatin show that in this case, owing to the presence of neutral salts the swelling is a function of the volume as well as the concentration of acid. Both results are predicted by the Procter-Wilson-Loeb theory of the swelling of gelatin.     

Regulation of the Epithelial Na+ Channel by Membrane Tension

The sensitivity of αβγ rat epithelial Na⁺ channel (rENaC) to osmotically or mechanically induced changes of membrane tension was investigated in the Xenopus oocyte expression system, using both dual electrode voltage clamp and cell-attached patch clamp methodologies. ENaC whole-cell currents were insensitive to mechanical cell swelling caused by direct injection of 90 or 180 nl of 100-mM KCl. Similarly, ENaC whole-cell currents were insensitive to osmotic cell swelling caused by a 33% decrease of bathing solution osmolarity. The lack of an effect of cell swelling on ENaC was independent of the status of the actin cytoskeleton, as ENaC remained insensitive to osmotic and mechanical cell swelling in oocytes pretreated with cytochalasin B for 2–5 h. This apparent insensitivity of ENaC to increased cell volume and changes of membrane tension was also observed at the single channel level in membrane patches subjected to negative or positive pressures of 5 or 10 in. of water. However, and contrary to the lack of an effect of cell swelling, ENaC currents were inhibited by cell shrinking. A 45-min incubation in a 260-mosmol solution (a 25% increase of solution osmolarity) caused a decrease of ENaC currents (at −100 mV) from −3.42 ± 0.34 to −2.02 ± 0.23 μA (n = 6). This decrease of current with cell shrinking was completely blocked by pretreatment of oocytes with cytochalasin B, indicating that these changes of current are not likely related to a direct effect of cell shrinking. We conclude that αβγ rENaC is not directly mechanosensitive when expressed in a system that can produce a channel with identical properties to those found in native epithelia.     

TEMPERATURE CHARACTERISTICS FOR THE OXYGEN CONSUMPTION OF GERMINATING SEEDS OF LUPINUS ALBUS AND ZEA MAYS

The rate of oxygen consumption by germinating seeds of Lupinus albus and of Zea mays was studied as a function of temperature (7–26°C.). The Warburg manometer technique was used, with slight modifications. Above and below a critical temperature at 19.5°C. the temperature characteristic for oxygen consumption by Lupinus albus was found to be µ = 11,700± and 16,600 respectively. The same critical temperature was encountered in the case of Zea mays, with temperature characteristics µ = 13,100± above and µ = 21,050 below that temperature.     

PULSATION OF THE CONTRACTILE VACUOLE OF PARAMECIUM AS AFFECTED BY TEMPERATURE

1. The rate of pulsation of the anterior contractile vacuole of Paramecium caudatum under chloretone anesthesia has been determined over a range of temperatures from 9–31°C. It has been found that the rate is a logarithmic function of the temperature according to the Arrhenius equation. From 9–16° the temperature characteristic (µ) has the value 25,600; from 16–22° it is 18,900; and from 22–31° it becomes 8,600. 2. It is concluded that there are at least three underlying reactions responsible for pulsation, the rates of which vary. Which reaction becomes the limiting one depends upon the range of temperature considered. 3. It does not appear that oxidative processes alone determine the rate of pulsation, although they may be of fundamental importance.     

THE SWELLING OF ISOELECTRIC GELATIN IN WATER : II. KINETICS.

It has been assumed that gelatin consists of a network of an insoluble material enclosing a solution of a more soluble material. The swelling of gelatin is therefore primarily an osmotic phenomena in that the water tends to diffuse in owing to the osmotic pressure of the soluble material. This osmotic pressure is opposed by the elasticity of the insoluble constituent, and equilibrium results when these two pressures are equal. The rate of the entrance of water should then obey Poiseuille''s law, provided the variable terms are expressed as functions of the volume. Equations have been derived in this way which agree quite well with the experimental curves and which predict the proper relation between the size and shape of the block and the rate of swelling. They lead to a value for the rate of flow of water through gelatin which has been checked by direct measurement. The mechanism assumed predicts that at a higher temperature and under conditions such that the water has to pass through collodion before reaching the gelatin, the experiment should follow the same course as that of osmosis discussed previously. This was also found to be the case. The slow secondary increase in swelling is ascribed to fatigue of the elastic properties of the gelatin. The rate of this secondary swelling should therefore be independent of the size of the block, in contrast to the rate of primary swelling which is inversely proportional to the size. It can further be shown that this secondary swelling should be proportional to the square root of the time, and also that with large blocks at higher temperatures the entire swelling should be of this secondary type. These predictions have also been found to be true.     

THE RECIPROCAL RELATION BETWEEN THE OSMOTIC PRESSURE AND THE VISCOSITY OF GELATIN SOLUTIONS

1. These experiments confirm the conclusion that protein solutions are true solutions consisting of isolated ions and molecules, and that these solutions may or may not contain in addition solid submicroscopic particles capable of occluding water. 2. The typical influence of electrolytes on the osmotic pressure of protein solutions is due to the isolated protein ions since these alone are capable of causing a Donnan equilibrium across a membrane impermeable to the protein ions but permeable to most crystalloidal ions. 3. The similar influence of electrolytes on the viscosity of protein solutions is due to the submicroscopic solid protein particles capable of occluding water since the amount of water occluded by (or the amount of swelling of) these particles is regulated by the Donnan equilibrium. 4. These ideas are supported by the fact that the more the submicroscopic solid particles contained in a protein solution or suspension are transformed into isolated ions (e.g., by keeping gelatin solution for 1 hour or more at 45°C.) the more the viscosity of the solution is diminished while the osmotic pressure is increased, and vice versa.     

THE DIFFUSION OF CARBON DIOXIDE IN TISSUES

1. Two methods are given for measuring the rate of diffusion of CO₂ in tissue membranes. Methods are also given for the determination of tissue thickness and the absorption coefficient for CO₂ in tissues. 2. The values obtained for the permeability constant (P x 10⁴) at 22°C. for CO₂ in the following tissues are:—frog skin, 3.05; connective tissue (dog), 2.65; smooth muscle (cat), 5.00; frog muscle, 5.29; striated muscle (dog), 4.70. P is expressed as cc. per cm.² per minute under a pressure gradient of one atmosphere per cm. 3. Evidence is presented to show that in a "steady state" bicarbonate contributes a negligible amount to the diffusion of CO₂. 4. The absorption coefficient for CO₂ in frog skin is 0.73 cc. per cc. and for frog muscle 0.78 cc. per cc. 5. In all of the tissues studied the diffusion of CO₂ is slower than in water. The diffusion coefficients (K x 10⁴ in cm.²/minute) at 22°C. for tissues as compared with water are:—water (16°C.), 9.5 (Hüfner, 1897); frog skin, 4.1; connective tissue, 3.7; frog muscle, 6.8; striated muscle (dog), 6.0; smooth muscle (cat), 6.4. 6. The time course of saturation of a tissue with CO₂ is altered in the presence of available base. Non-acidified tissues saturate more slowly than acidified tissues and the rate of saturation is dependent on the CO₂ tension.     

THE EFFECT OF TEMPERATURE UPON SOME OF THE PROPERTIES OF CASEIN

1. The investigations dealing with the properties of casein as an acid were reviewed. 2. The solubility of uncombined casein in water was measured at 5°C. and found to be 0.70±0.1 mg. of N per 100 gm. of water. 3. Robertson''s solubility measurements of casein in bases at various temperatures were recalculated and found to agree well with more recent measurements. 4. By combining the observations of several investigators, as well as the author''s measurements of the solubility of casein, in base, at various temperatures, the following conclusions were reached: (a) The solubility of casein in base is affected by the temperature in a discontinuous manner. (b) There exist two ranges of temperature, one, extending from about 21° to 37°C. and the other from about 60° to 85°C. where the solubility of casein in base is practically independent of temperature. (c) From 37° to 60° the equivalent combining weight of casein rises from the value 2100 to about 3700 gm. 5. By comparing the values of base bound by 1 gm. of casein at the two temperature ranges with a constant, the value of base necessary to saturate the same amount of casein, it was found that the latter value is a common multiple of the former values, indicating the stoichiometric nature of the effect of temperature.     

FRACTIONATION OF GELATIN

1. It is possible to fractionate gelatin by means of reprecipitation at 23°C. of a salt-free solution of pH 4.7 into two fractions, one of which is soluble in water at any temperature, and a second one which does not dissolve in water even when heated to 80°C. 2. The proportion of the soluble fraction in gelatin is much greater than of the insoluble one. 3. The insoluble fraction of gelatin does not swell when mixed with water, but it does swell in the presence of acid and alkali which finally dissolve it. 4. Blocks of concentrated gel made by dissolving various mixtures of the soluble and insoluble fractions of gelatin in dilute NaOH swell differently when placed in large volumes of dilute buffer solution pH 4.7 at 5°C. The gel consisting of the insoluble material shows only a trace of swelling, while those containing a mixture of soluble and insoluble swell considerably. The swelling increases rapidly as the proportion of the soluble fraction increases. 5. A 5 per cent gel made up by dissolving the insoluble fraction of gelatin in dilute NaOH loses about 70 per cent of its weight when placed in dilute buffer pH 4.7 at 5°C. A similar gel made up of ordinary gelatin loses only about 20 per cent of its weight under the same conditions. 6. It was not found possible to resynthesize isoelectric gelatin from its components. 7. An insoluble substance similar in many respects to the one obtained by reprecipitation of gelatin is produce on partial hydrolysis of gelatin in dilute hydrochloric acid at 90°C.     

THE GROWTH AND DURATION OF LIFE OF CELOSIA CRISTATA SEEDLINGS AT DIFFERENT TEMPERATURES

Daily measurements of hypocotyl length were made on Celosia cristata seedlings cultured in darkness under aseptic conditions at six constant temperatures between 14.5° and 40.5°C. At 40.5° roots did not penetrate the agar and only the hypocotyls that were supported by the wall of the test tube could be measured. The growth curves were of the generalized logistic type, but of different degrees of skewness. The degree of symmetry of the growth curves was influenced by temperature. At the lower temperatures the maximal growth rate came relatively late in the grand period of growth; at successively higher temperatures it came progressively earlier. The mean total time rate of growth (millimeter per diem) was found to be a parabolic function of the temperature. The maximum rate of growth was found from the curve to be at 30.48°C. The maximum observed rate of growth, and the maximum yield, were found to be at 30°C. At all temperatures above 14.5° the maximum growth activity fell in the second quarter of the whole growth period. At all temperatures tested other than 30°, and at all parts of the growth cycle, the growth yield as measured by height of hypocotyl at any given equivalent point was less than at 30°. The total duration of life of the seedlings, and the duration of life after the end of the growth period (intermediate period) were inversely proportional to the mean total growth rate. The observations on Celosia cristata seedlings are thus in accord with the "rate of living" theory of life duration. The optimal temperature for life duration is the minimum temperature, within the range of these observations.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : IX. WATER UPTAKE AND SWELLING OF COLLODION MEMBRANES IN AQUEOUS SOLUTIONS OF ORGANIC ELECTROLYTES AND NON-ELECTROLYTES

1. Dried collodion membranes are known to swell in water and to the same limited extent also in solutions of strong inorganic electrolytes (Carr and Sollner). The present investigation shows that in solutions of organic electrolytes and non-electrolytes, the swelling of dried collodion membranes is not as uniform, but depends on the nature of the solute. 2. The solutions of typically "hydrophilic" substances, e.g., glycerine, glucose, and citric acid, swell collodion membranes only to the same extent as water and solutions of strong electrolytes. In solutions of typically carbophilic substances (e.g., butyric acid, valeric acid, isobutyl alcohol, valeramide, phenol, and m-nitrophenol) the swelling of the membranes is much stronger than in water, according to the concentration used. For the brand of collodion used the swelling in 0.5 M solution was in some cases as high as 26 per cent of the original volume, as compared to 6 to 7 per cent in water. Therefore, in these solutions the "water-wetted dried" collodion membrane is not rigid, inert, and non-swelling, but behaves as a swelling membrane. 3. The solutes which cause an increased swelling of the membranes are accumulated in the latter, the degree of accumulation being markedly parallel with the degree of their specific swelling action. 4. The anomalously high permeabilities of certain carbophilic organic solutes reported by Michaelis, Collander, and Höber find an explanation in the specific interaction of these substances with collodion. 5. The use of the collodion membrane as a model of the ideal porous membrane is restricted to those instances in which no specific interaction occurs between the solute and the collodion.