A Physiological Solution for Freshwater Crustaceans

Contrary to what we know of the nerve muscle preparation of the frog, the irritability of the nerve of a freshwater crustacean quickly disappears on bathing it in an isotonic sodium chloride solution. For marine crustaceans seawater may be used successfully as a physiological solution. For Astacus fluviatilis, Hoffmann's formula, a solution of about twice the concentration of the Ringer solution for the frog, has generally been employed. With such solutions the results with nerve muscle preparations have not been very satisfactory (Hoffmann, Segaar). With the crustacean heart, however, the results have been better (Potioné, Lindemann). An attempt was made to find a better physiological solution for the freshwater crayfish.Two species of freshwater crustaceans, Astacus trowbridgii and Cambarus clarkii were investigated. The freezing point of the blood was determined in order to know the molecular concentration. The amount of the physiologically important ions, Ca, K and Mg was estimated, and finally the pH was determined. As even large specimens do not give more than .5 to 1 cc. of blood, the blood of 8 to 10 crayfishes was collected and mixed, and all the estimations except the pH were done with this. The figures obtained in this way are thus averages, for our purpose not a disadvantage. The blood was collected by sucking it out of the pericardial cavity which surrounds the heart ventricle, with a paraffined hypodermic syringe. The blood for the Ca, K and Mg determination and for the freezing point was cooled to 0° and stirred for about 15 minutes to prevent clotting. After centrifuging a clear serum was obtained. The blood for the pH determination was collected in a small amount of a 1% potassium oxalate solution under a layer of liquid paraffin, to avoid loss of CO.