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A brief review is given of existing knowledge regarding the physiological effects of anions, and literature dealing with their relative toxicity. The degree of toxicity of twenty-seven anions to Polycelis nigra (Müller) has been assessed, by determining in each case the molar concentration the animal survives for 48 hr. at 15−18° C. On this basis their order of increasing toxicity is as follows; commas separate ions of similar degree of toxicity: Generally speaking anions are very much less toxic than cations. Even the most toxic anion (OH) is far less toxic than ionic copper, silver or gold. The respiration rate of Polycelis is heavily depressed by cyanide, but the survival time is three days or longer, as long as the respiration rate is not less than about 16 % of the normal value. With further depression the survival time shortens rapidly, and at 9 % normal is under 4 hr. The normal respiration rate of Polycelis nigra is 0·165 c.c. O2/g./hr. This is not very much less than that of the trout. Polycelis is considerably the more resistant to cyanide. This is probably connected with its capability of surviving very many hours in water containing a very reduced supply of oxygen.

Lethal concentration limits have been determined for the hydrogen ion and the ions of eighteen metals. The three-spined stickleback (Gasterosteus aculeatus L.) has been employed as test animal. According to their lethal concentration limits on a mg./l. basis their order of increasing toxicity is : Sr Ca Na Ba Mg K Mn″ Co″ Cr″ Ni″ Au″ Zn Cd″ Pb″ Al Cu″ H Hg″ Ag. On a molar concentration basis the order is as follows: Na Ca Sr Mg Ba K Mn″ Co″ Cr″′ Ni″ H Zn Al Au″′ Cd″ Pb″ Cu″ Hg″ Ag. All these ions, with the exception of the first six (the metals of the alkalis and alkaline earths), bring about the death of fish by precipitating the gill secretions, thus causing asphyxiation. The alkali and alkaline earth metals appear to enter the body and act as true internal poisons. The position of iron is uncertain. The toxicity of solutions of iron salts appears to be due, mainly if not entirely, to their acidity. On a mg./l. or molar concentration basis there is a marked relationship between the toxicity of the metals and their solution pressures. The metals of very low solution pressure (Ag, Cu, etc.), i.e. those whose ions are most ready to part with their charges and enter into combination with other ions or compounds, are the most toxic as they precipitate the gill secretions and bring about asphyxiation with extreme rapidity. Metals of somewhat higher solution pressure (Zn, Pb, Cd) act in the same way but more slowly. Manganese, which of all the heavy metals has the highest solution pressure, takes effect very slowly and the ions of the alkali and alkaline earth metals, which have a high affinity for their charges, do not precipitate the gill secretions at all. In the case of all the ions other than those of the alkali and alkaline earth metals the reactions responsible for the death of the fish take place outside the body. Thus their speed of action does not depend on their penetrating power and the permeability factor does not enter. This is probably responsible in great measure for the good agreement observed between their toxicity and their affinity for their electrical charges.

This paper presents the results of about 100 experiments to test the reactions of small fish to water of low oxygen concentration, using an apparatus similar to that previously employed by the writer to study the reactions of fish to toxic solutions. At 13 ° C. the stickleback (Gasterosteos acoleatos) has no immediate appreciation of water of low oxygen concentration and will swim into it with no hesitation. If the fish remains in the poorly oxygenated water respiratory distress develops, accompanied by uneasiness and random movement. When this random movement takes the animal back into the well-oxygenated water the stimulus to swimming vanishes, the fish stops moving and quickly recovers. Over a wide concentration range at 13 ° C. the reaction takes 1 · 3 min. At 3 ° C. the reaction is very slow, taking 5-6 min. even when the water contains only 0 · 3 mg./l. of oxygen. At 20 ° C. and oxygen concentrations below 2 mg./l. the response is very prompt, respiratory distress developing so quickly that the fish usually will not swim into the poorly oxygenated water, but turns away from it or swims backwards; it may make repeated attempts to enter the low-oxygen zone, retreating each time as if violently irritated. Experiments with minnows (Phoxinus phoxinus’) and trout fry (Salmo truttà) gave generally similar results. Here again the essential factor appears to be the speed with which dyspnoea develops.

This paper records some observations on the reactions of minnows to phenolic substances. The fish are placed in a horizontal tube, half of which is filled with flowing water and half with flowing solution of the concentration to be tested. Water and solution are very sharply differentiated. Solutions of phenol, ortho- and para-cresol are highly toxic and appear to have some specific effect on the nervous system of fish, causing them to lose their sense of balance and capability of co-ordinated movement. The time the solutions take to produce this effect is much shorter than the survival time; in a 0.01% solution of para-cresol, for example, a minnow loses its sense of balance in about 70 sec. but takes about 30 min. to die. Over the concentration range 0.04-0.0004% minnows appear to have little or no power of discriminating between phenol and water, swim into the solution and become intoxicated. At concentrations of 0.03-0.04% minnows will avoid para-cresol and ortho-cresol solutions immediately and escape intoxication. At somewhat lower concentrations the fish venture into the solution, and this quickly destroys their capability of recognizing and avoiding it. The situation is markedly different from that observed in the case of lead and zinc salts; here the time the fish takes to establish an avoiding reaction to the solution is very much shorter than the time this takes to destroy its capability of doing so.

The degree of toxicity of the hydrogen ion and the ions of eighteen metals to Polycelis nigra (Müller) has been assessed by determining in each case the concentration the animal survives for approximately 48 hr. at 15-18° C. On a mg./I. basis their order of increasing toxicity is: Sr Na Ca Mg Mn″ Pb″ K Al Co″ Cr‴ Ni″ As‴ Zn Cd″ H Au‴ Cu″ Hg″ Ag On a molar concentration basis the order is as follows : Na Sr Ca Mg Mn″ K Al Pb″ Cr‴ Co″ Ni″ H As‴ Zn Cd″ Cu″ Au‴ Ag Hg″ The position of iron is uncertain; the toxicity of ferric chloride solutions appears to be due to their acidity. Irregular results were obtained with solutions of barium salts, which appear to effect excessive stimulation of the musculature of the animal and induce convulsive movements which eventually result in the rupture of the body and extrusion of the tissues. On a mg./l. or molar concentration basis there is a decided relationship between the solution pressures of the metals and the degree of toxicity of their salts, the general result being very similar to that obtained in an earlier investigation with Gasterosteus aculeatus as test animal. This relationship suggests that the degree of toxicity of ions is largely determined by their affinity for their electrical charges, this affinity determining the readiness with which they tend to abandon the ionic state to enter into chemical combination with protoplasmic compounds.

Mercuric chloride, one of the most toxic of inorganic substances, does not ionize in aqueous solution, but in the presence of sodium chloride forms the double chlorides NaHgCl3 and Na2HgCl4 which ionize readily. It has been variously claimed that the ionization of mercuric chloride, thus effected, is accompanied by an increase of toxicity, by a decrease of toxicity, or that the toxicity of the solution remains unaltered. In an investigation of the toxicity of mixed solutions of HgCl2 and NaCl to the minnow, Phoxinus phoxinus (L.), it is found that the addition, to HgCl2 solutions, of sufficient NaCl to convert the whole of the HgCl2 into the double chloride Na2HgCl4, and even ten times this quantity of NaCl effects no marked change in the toxicity of the solution. On the addition of a considerable excess of NaCl a marked prolongation of the survival time occurs, the maximum antagonistic effect being evident when the solution is approximately isotonic. Almost exactly the same result is obtained if the NaCl is replaced by quantities of glucose sufficient to effect equal changes in the osmotic pressure of the solutions, and thus the antagonistic action of the sodium chloride appears to be due to the physical, rather than the chemical, changes its addition brings about in the nature of the toxic solution.

A brief review is given of previous work on the toxic effect of aqueous solutions of metallic salts on living protoplasm and fresh-water animals. The behaviour of Polycelis nigra in aqueous solutions of metallic salts is described, survival curves for this animal in some variety of salts are given, and the mode of toxic action of these salts is discussed. It is shown that in the case of heavy metal salts the toxic effect at concentrations below isotonicity is due almost entirely to the cation, the toxicity of the anion being relatively small. At concentrations above isotonicity the anion and the osmotic pressure of the solution act as additional lethal factors. Salts of the metals of the alkalis and alkaline earths are shown to be comparatively harmless below isotonicity, with the exception of salts with a toxic anion such as potassium chromate. This salt is highly toxic at low concentrations. It is shown that in the case of the nitrates and sulphates of the heavy metals, the toxicity is determined by the product of the normality and the electrical conductance ratio at that normality. Recovery experiments with Polycelis are described and it is shown that these illustrate the above relationship between toxicity and conductivity. Survival curves for Gammaruspulex in salts of copper and zinc are described. Those for zinc exhibit the same relationship.

A brief review is given of the various types of living material and of toxic substances employed by different workers in the study of antagonism. Survival curves are described for the heavy metal salts nickel nitrate, copper nitrate and cadmium nitrate, and the alkaline-earth metal salts magnesium, calcium, strontium and barium nitrate, for the tadpole of the toad, Bufo bufo bufo (L.). A description is given of Osterhout’s method for the detection and measure-ment of antagonism by observing the effect of mixing, in varying proportions, equally toxic solutions of the two substances in question. Survival curves for tadpoles in mixtures of equally toxic solutions of nickel nitrate and strontium nitrate indicate marked antagonistic action between these salts, the effect increasing with dilution. The survival curve for mixtures of the equally toxic solutions 0·03 N copper nitrate and 0·40N strontium nitrate apparently indicate antagonism over a part of the concentration range and synergism over the remainder. This is because a 0·03 N solution of copper nitrate increases in toxicity upon dilution, its toxicity reaching a maximum at approximately 0·0015N. If the normality of the copper solution is below this critical value its mixture with an equally toxic strontium solution gives a normal antagonism curve. It is shown that the other alkaline-earth metals, calcium, magnesium and barium also reduce the toxicity of copper solutions. The strontium concentration— copper concentration—survival time relationship is studied in detail and the way in which the survival time locus is represented by a curved surface is described. The survival surfaces for copper and calcium, copper and magnesium and copper and barium are of similar type. Problems for further investigation arising out of the results are briefly discussed.

Lethal limits of concentration are determined for lead, zinc and copper for the three-spined stickleback (Gasterosteus aculeatus L.). The addition of calcium salts to solutions of lead nitrate or zinc sulphate reduces the toxicity of these salts to Gasterosteus. 50 mg. per 1. of calcium (as nitrate or chloride) is sufficient to annul the toxicity of a 1 × 10−6 g. per c.c. solution of lead or a 2 × 10−6 g. per c.c. solution of zinc. The reactions of the fish in the solutions with and without calcium are compared, and the respiratory symptoms are described with the aid of graphs illustrating the variation in respiration rate during the survival time. It is shown that a running supply of “hard” tap water containing approximately 50 mg. per 1. of calcium as calcium bicarbonate is harmless to the minnow, Phoxinusphoxinus (L.) and to the stickleback, when there is added to it the maximum amount of lead that it can hold in solution (7 ×10−7g. per c.c.). This concentration of lead in soft water is fatal to Gasterosteus in 3812 hr. The same amount of calcium renders a 10 × 10−6 g. per c.c. solution of lead harmless to the goldfish, Carassius auratus (L.). It is concluded that, in the presence of sufficient calcium, the interaction between the lead, or zinc, and the mucus secreted by the fish does not take place. This conclusion was endorsed by experiments in vitro on the slime secreted by the eel, Anguilla anguilla (L.). The application of these results to the pollution of natural waters by effluents from lead and zinc workings is briefly discussed.