An elucidation of the mechanisms of chromatophore control in teleost fishes involves consideration of the participation of the nervous system (pigment concentrating and dispersing fibers) and an evaluation of influences mediated by pituitary hormones. The sand flounder, Scopthalamus aquasus Norman (Lophosetta muculatu Gill) was investigated by neurological and pharmacological methods. Nerve cutting, blocking and stimulation experiments revealed unequivocally functional pigment aggregating but not dispersing fibers. Acetyl choline and eserine when injected into the spinal cord bring about excitation of pigment concentrating nerve fibers but have no local effect on melanocytes. Drugs causing local pigment aggregation are aromatic ethyl amines or hydrazines. Epinephrine, norepinephrine and dopamine are extremely active. The most potent pigment dispersing drugs were certain phenothiazine tranquilizers. Pretreatment with pyrogallol markedly potentiated epinephrine and norepinephrine but raised the effective dose of five of the drugs having pigment dispersing properties. The pharmacological data suggest a catechol amine as the transmitter at concentrating nerve fiber endings, and that the enzyme catechol‐o‐methyl transferase is involved in the physiology of color change in the sand flounder.

1. Methods for the use of the marine green alga, Ulva lactuca, in studies on electrolyte metabolism are described. 2. The effect of illumination and iodoacetate on the potassium and sodium content, as well as the influence of light and running sea water on the iodoacetate effect was investigated. The rate of exchange of cellular potassium ion for K42 under conditions of light and dark at 20 and 30°C. was studied. 3. Ulva maintained in the dark for long periods loses some potassium and gains sodium, both effects being reversed upon illumination. The presence of 0.001 M iodoacetate in the dark causes a marked progressive loss of potassium and gain of sodium, phenomena which do not occur when the alga is illuminated. Evidence for the penetration of the inhibitor into the cell in the presence of light is presented. The iodoacetate effect on potassium and sodium content, once established, can be "washed out" of the alga when the plant is placed in light and running sea water without the inhibitor. Illumination and increased temperature each favor a more rapid exchange of tissue for environmental potassium ion. 4. In the interpretation of these findings it is emphasized that metabolic work, perhaps in the form of ion transports, must be done by the cell to compensate for the continual flow of potassium ion and sodium ion with their respective concentration gradients and thus maintain homeostasis within the cell. Evidence is presented which indicates separate mechanisms for the distribution of sodium and potassium in this organism. It is further suggested that the degradation of phosphoglyceric acid, an important glycolytic and photosynthetic intermediate, or one of the products of its metabolism supplied the energy for these ion transports(s). The role of permeability per se is considered.

The inorganic composition of living cells is regulated by a selective a h -r p t i o n process which undoubtedly is intimately associated with metabolism. The mineral environment, however, may influence the absorption of electrolytes by effecting a shift in metabolism itself (Steward and Preston, '41), or, as recent data seem to indicate, by direct chemical interaction of environmental cations with cellular constituents. A systematic study of the relationship of the electrolytic environment to the chemical composition of living organisms reveals the degree to which the surrounding medium may determine the concentration of intra-cellular mineral elements.Chlorella pyrenoidosa is found in most naturally occurring bodies of fresh water. Consequently this unicellular algal cell can adjust to a considerable variation in its mineral environment. This paper reports a study of the extent to which the amount of calcium, magnesium, potassium, sodium and phosphorus in this plant cell varies as the concentration of the various cations in the culture medium are altered. MATERIALS AND METHODSThe original cultures of Chlorella pyrenoidosa were obtained in 1937 from the laboratory of C. B. Van Niel. The strain was isolated and identified by Dr. Robert Emerson.Pure stocks of Chlorella pyrenoidosa were maintained on washed agar slants enriched by Detmer's inorganic medium. For tests of purity of the stocks, streaks were made from time to time on agar slants containing, in addition to Detmer's medium, glucose and peptone added in concentrations of 2% and 0.5% respectively. On such a substrate bacterial or mold contaminants became apparent through their rapid overgrowth of the Chlorella. The mass culture method developed by Ketchum and Redfield ( '38) for marine diatoms has been further refined and adapted to the growth of Chlorella. The cultures are grown in large Pyrex bottles containing 10 or 12 liters of Detmer 's medium of the following composition :