1. All inorganic perfusing solution for the heart of the lobster Homarus americanus , to allow prolonged normal beating (20 hours or more) must agree closely with the inorganic composition of the serum, which varies differentially with that of the environmental sea water. 2. All of the chief inorganic ions of the serum are necessary—Na, K, Ca, Mg, Cl, and SO 4 ; the critical numbers of the ions being 100, 3, 5, 2–3, 116, and 1–2 respectively. Absence of Mg and SO 4 will be tolerated for several hours. 3. The pH of the solution must agree with that of the serum within 0.2. 4. The osmotic pressure of the solution must agree with that of the serum within 15 per cent. 5. Beating of the heart will continue for several hours on improperly balanced solutions but changes in frequency, tone, or amplitude will occur. Hearts adapted to such solutions will show different responses to physical and chemical stimuli of the solution than those perfused on properly balanced solutions. 6. Arrest in systole is caused by isotonic NaCl, KCl, LiCl, and urea, and arrest in diastole by isotonic CaCl 2 , MgCl 2 , NaBr, NaI, MgSO 4 , and glucose. 7. Lithium cannot replace sodium; neither can bromide or iodide replace chloride ions.

1. The electrolyte composition, the pH, and freezing points of the fluids of several invertebrates and one primitive chordate are reported. 2. Fluids of the worms, echinoderms, and the clam Venus were isotonic with sea water; fluids of the Arthropoda were hypertonic to sea water. 3. The pH of all fluids was below that of sea water. In the Arthropoda and Myxine less individual variation in pH appeared than in the echinoderms and worms. 4. Ratios of ionic concentrations in the fluid to those in the sea water indicated (1) uniform distribution of ions between the internal and external media for the echinoderms and Venus , (2) differential distribution of potassium and magnesium in the worms; (3) differential distribution of sulfate, magnesium, potassium, and calcium in the Arthropoda; and (4) differential distribution of calcium, magnesium, and sulfate in Myxine . 5. The unequal distribution of ions implies the expenditure of energy against a concentration gradient across the absorbing or excreting membranes, a capacity frequently overlooked in the invertebrates. 6. The sera of the Arthropoda from diluted sea water showed higher concentrations of sodium, potassium, calcium, and chloride ions relative to the respective concentrations in the external medium than in normal sea water, and also showed different orders for those ions. 7. The increase in osmotic pressure of the sera of the animals moving into brackish water is caused by unequal accumulation of sodium, potassium, calcium, and chloride ions. Sulfate and magnesium ionic ratios do not change.

1. Fundulus heteroclitus was found to be a reliable experimental animal for studies on chemical stimulation in either fresh or sea water. 2. The response of Fundulus to hydrochloric, acetic, propionic, butyric, valeric, and caproic acids was determined in fresh water, while the same acids plus sulfuric and nitric, as well as the sodium salts of the mineral acids, were tested in sea water. 3. Stimulation of Fundulus by hydrochloric acid in fresh water is correlated with the effective hydrogen ion concentration. Stimulation by the n -aliphatic acids in the same environment is correlated with two factors, the effective hydrogen ion concentration and the potential of the non-polar group in the molecule. However, as the number of CH 2 groups increases the stimulating effect increases by smaller and smaller amounts, approaching a maximum value. 4. Stimulation of Fundulus by hydrochloric, sulfuric, and nitric acids in sea water is correlated with the forces of primary valence which in turn are correlated with the change in hydrogen ion concentration of the sea water. The n -aliphatic acids increase in stimulating efficiency in sea water as the length of the carbon chain increases, but a limiting value is not reached as soon as in fresh water. 5. Only a slight difference in stimulation by hydrochloric acid is found in sea water and in fresh water. However, there is a significant difference in stimulation by the fatty acids in fresh and in sea water, which is partly explained by the different buffering capacities of the two media. It is to be noted that in the same environment two different fish, Fundulus and Eupomotis , give different results, while the same fish ( Fundulus ) in two different environments responds similarly to mineral acids but differently to fatty acids. These results illustrate that stimulation is a function of the interaction between environment and receptors, and that each is important in determining the response. 6. Stimulation by sodium chloride, nitrate, and sulfate is correlated with equivalent concentrations of the salts added to sea water, or with the forces of primary valence. Although the threshold for stimulation by the salts is considerably higher than for the acids, the efficiency of stimulation by the salts is greater.

1. Stimulation in the rock barnacle Balanus balanoides by hydrochloric, sulfuric, and nitric acids, and by the first seven members of the normal aliphatic acid series has been studied. The hydrogen ion concentrations of the solutions tested varied from 3.2 x 10 –8 to 5.889 x 10 –6 . The criterion of response was percentage closure in groups of individuals, recorded at 1 minute intervals until maximum closure occurred. 2. The intensity of stimulation by these acids is proportional to the effects of two forces, one related to the change in the (H + ), and the other to the field of force around the anion of the acid added to the environment. 3. A preliminary interpretation of the results led to the development of the following expression which fits approximately the data obtained at the end of 4 minutes: Per cent closure = 100 – 100 e –0.1 z +(0.003125)2 –0.1 z +(0.003125)2 n ( z –0.4) where z is the (H + ) x 10 7 and n is the number of carbon atoms (if present) in the anion of the acid. This equation assumes that the anions of the mineral acids enter into the reaction stoichiometrically, and emphasizes the difference in the fields of force around the anion of the fatty acids, a difference which is correlated with the length of the carbon chain. 4. A further analysis of the data revealed the presence of three or more receptor groups which appeared to be differentially affected by forces originating from the anions of the acids. 5. The order of stimulating efficiency for the mineral acids was found to be: HCl>H 2 SO 4 >HNO 3 . 6. The order of stimulating efficiency for the fatty acids was found to be: heptylic>caproic>valeric>butyric = acetic>propionic = formic.

1. The stimulating efficiency of hydrochloric, sulfuric, and nitric acids has been measured in the sunfish Eupomotis gibbosus , by a method which reduces experimental errors to a minimum. 2. The results show that stimulation by these acids is primarily dependent upon the (H + ) produced in the animal's aquatic environment, and that the reaction time is a logarithmic function of the (H + ) within the range tested expressed by the equation: ( RT –5) = –4.3 log (H + x 10 4 ) + 9.118. 3. Any effect of the chloride, sulfate, and nitrate ions must itself be measured by the (H + ). 4. Variation in the reaction time is also a logarithmic function of the (H + ), and the percentage variation is independent of the (H + ) over the range tested. 5. Freshly collected fish show a lower threshold for stimulation as determined by the (H + ) than do fish adapted to laboratory conditions, but relatively the reaction times of the two groups are the same.

In Vol. 15 , No. 6, July 20, 1932, page 620, in the first line under References, for J. Gen. Physiol., 1931–32 , 15 , 62 , read J. Gen. Physiol., 1931–32 , 15 , 621 .

1. Stimulation in the rock barnacle Balanus balanoides by the sodium salts of the first seven normal aliphatic acids has been studied at several different concentrations for each salt. The pH was adjusted to that of sea water (8.1 ±0.15) and all experimental conditions were held as constant as possible. Criterion of response was the per cent closure of valves at successive 2 minute intervals. 2. In general, the stimulating efficiency increases with concentration, but the ratios of effectiveness at increasing concentrations differ for each salt. 3. The order of effectiveness for 40 to 50 per cent closure is: heptylate = caproate > valerate > butyrate > formate > propionate > acetate. For 60 per cent closure or more, formate is the least effective of all. 4. Stimulating efficiency is correlated with the potential of the anion of the acid and with the concentration of that ion near or at the receptor surface as determined by the length of the carbon chain.

1. The reaction of the catfish, Schilbeodes gyrinus Mitchill, to hydrochloric acid over a wide range of concentrations (from pH 1.82 to pH 6.83) has been studied under experimental conditions which reduced to a minimum all other stimuli. 2. As the [H + J increases within the limits mentioned, the reaction time of the fish decreases. In other words, the rate of the stimulation processes is an increasing function of the hydrogen ion concentration. 3. The effective stimulus is the hydrogen ion, since NaCl solutions of equivalent concentration were not stimulating. 4. Stimulation by hydrochloric acid is therefore correlated with the potential of the cation resulting from dissociation of the acid molecule.

In Vol. 14, No. 1, September 20, 1930, page 85, in the next to the last line, under References, for Amer. J. Physiol., 1918, 14, 315 ; read Amer. J. Physiol., 1918, 45, 323 .

1. The stimulating efficiencies of some normal primary aliphatic alcohols have been determined for the barnacle, the frog, and Planaria , under conditions which do not involve narcosis or simultaneous stimulation by other agents. 2. Concentrations of the successive alcohols necessary to produce a given stimulatory effect vary according to the following geometrical series: 1: a –1 : a –2 : a –3 : a –4 : . . . ., where a represents some real number. 3. Within certain limits the relationship between the logarithm of the concentration necessary to produce a given effect and the reciprocal of the reaction time is linear in the frog and in Planaria . 4. The concentration effect may be expressed by an equation which contains one constant characteristic of the alcohol series, and another one characteristic of each member. The ratio of the latter constants for successive alcohols represents a in the above series. 5. The stimulation by alcohols in these animals is considered to be due to energy changes at the receptive surfaces, brought about by a definite orientation of the respective alcohol molecules. Increase in stimulating efficiency as the number of CH 2 groups increase must be due to the rôle of the non-polar portion of the alcohol molecule, since the polar group remains practically constant throughout the series. 6. In homologous series of organic compounds it is conceived that stimulating effects will be produced either by the polar group or the non-polar group, according to which one becomes dominant in effect, or to a combination of the two.

1. The relation of temperature to the pedal rhythm of Balanus balanoides L. has been studied under otherwise constant conditions. 2. The frequency of movement increases with temperature, showing three groups of thermal increments and three critical temperatures. Five animals yielded µ = 5,700 above 14.5° C. and 12,100 below; 3 gave µ = 7,800 above 9.3° and 22,500 below; while 9 showed µ = 9,500 above 8.1° and 22,100 below. 3. The upper critical temperatures, above which different effects appeared in different animals were 23.4°, 26.0°, and 27.0°. Above 27.0° none of the valves remained open. 4. Excepting the values 5,700 and 9,500, the increments are similar to those previously found to be associated with respiratory and with neuromuscular activities. 5. Dilution of the sea water with from 3 to 4 per cent fresh water decreases the rate without altering the increments. More than 4 per cent dilution causes irregularity.

A consideration of the temperature characteristics or thermal increments for locomotion in Planaria shows that they agree essentially with those reported for certain activities of other animals (Crozier, and Glaser). A process with the lowest increment (µ = 7,000 to 8,000) assumes control of the locomotor rate at temperatures above 20–22°; that with the highest increment (µ = 18,000 to 22,000) controls below 13°; and one with an intermediate value (µ = 11,100) is in command at the intermediate temperatures (13–21°). Another reaction with increment µ = 14,600 may, under certain conditions ( e.g . 2 weeks after feeding), control the series over the median range. Excepting the latter, these increments are typical of catalyzed oxidative reactions (Crozier 1924–25, b ) so that when these are in control it may be assumed that respiration is the fundamental process determining the rate of locomotion. Feeding produces a modification of the increment throughout the median range of temperatures, up to 2 days afterward.

1. The snail Helix aspersa Müller, is negatively geotropic during the daytime, but positive or indifferent at night. 2. The precision of geotropic orientation is a function of the gravity component acting on the body. 3. The rate of geotropic locomotion is also determined by the gravity component (sine of the angle of inclination). 4. The rate of upward movement is increased 1.51 times at 45° inclination by loading the snail with one-half its weight. No such increase is seen in loaded snails creeping on a horizontal surface. 5. Moderate centrifugation results in orientation and locomotion towards the center of rotation. 6. A response analogous to the homostrophic reflex occurs when a backward pull to right or to left is exerted on the shell. Bilaterally equal tension applied to the shell causes locomotion along a path parallel and opposite to the direction of the pull. 7. All the observations go to show that the stimulus for geotropic orientation and locomotion is tension of the body muscles produced by the downward pull of gravity, and that the stimulus is received by the proprioreceptors of these muscles. Otolith apparatus and analogous organs, when present, may assist in the response, but they do not seem to be requisite in all cases. Since the precision of orientation and the rate of locomotion are functions of the gravity component acting on the body, the muscle tension theory of the geotropic reactions accords fully with Loeb's tropism doctrine for animals.

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.

1. Under laboratory conditions Limulus from 20 to 60 mm. in diameter are positively phototropic, and execute circus movements towards the normal side, when the median and the opposite lateral eyes are removed or covered. 2. The phototropism of Limulus may be modified or obliterated by ( a ) fright, ( b ) hunger, ( c ) stereotropism, ( d ) photokinesis, and ( e ) unknown stimuli. 3. Quantitative measurements of the paths of animals doing circus movements demonstrate that the amount of turning varies directly with the light intensity as follows: for 8,000 candle meters the degrees turned per centimeter were 6.73; for 2,000 candle meters, 5.23; and for 900 candle meters, 4.78. In other words, the diameter of the circle varies inversely with the light intensity. 4. The rate of locomotion per minute also varies directly with the light intensity, being 178 cm. for 8,000 candle meters, 167 for 2,000, and 157 for 900. 5. These reactions are satisfactorily explained by the tropism theory.