THE HYDROGEN ION CONCENTRATION OF THE CONTENT OF THE FOOD VACUOLES AND THE CYTOPLASM INAMOEBAAND OTHER PHENOMENA CONCERNING THE FOOD VACUOLES

Abstract

1. In Amoeba new food vacuoles which contain chilomonads or colpidia decrease greatly in size and the organisms in them die soon after they have decreased to minimum; then the size increases rapidly and digestion begins, after which the size decreases very gradually. 2. If the culture fluid contains neutral red, the organisms in the vacuoles become purple (like buffer solution, pH 3.5, containing neutral red) immediately after they die, but the fluid around them remains colorless until after the vacuoles have increased in size, then it becomes yellow like buffer, pH 8, but the organisms in it remain purple for some time after this, then become brownish yellow. 3. The color of the organisms immediately after death in the food vacuoles is the same as that of organisms which have died in a solution of neutral red outside. This and the fact that the fluid in the food vacuole does not, at this time, become colored indicates that the acid originates in the vacuole, not in the cytoplasm around it. The fact that the fluid in the vacuole later becomes yellow before the organisms in it do, indicates that the base originates in the cytoplasm around the vacuole, not in the organisms in it. 4. Potato or wheat starch grains ingested by amoebae in culture fluid containing neutral red become purple like buffer, pH 2. This color is, however, largely a physical phenomenon, and therefore does not accurately indicate hydrogen ion concentration. 5. Neutral red crystals become pink and dissolve in buffer, pH 5, but they do not become pink and do not dissolve in the solution in the food vacuoles, either if they are alone or if they are in the vacuoles with organisms. This solution, therefore, does not become as strongly acid as pH 5. 6. Chilomonads killed in alkaline solution containing congo red are brilliant orange in color. They become bluish in buffer, pH 4 to 3.5. Amoebae ingest them readily. They remain orange in color in the food vacuoles. This shows that the acidity of the fluid in the vacuoles does not reach pH 4. 7. Chilomonads killed in alkaline solution of brom cresol purple are strongly purple. They become yellowish in buffer solution, pH 5.8 to 5.6. In the food vacuole they become slightly yellowish. This indicates that the acidity of the solution in the vacuoles reaches at least pH 5.6. 8. Results obtained with chilomonads killed respectively in cresol red and phenol red indicate that the maximum alkalinity of fluid in the food vacuoles is approximately pH 7.3. 9. The hydrogen ion concentration in the food vacuoles in Amoeba changes from about pH 5.6 to about pH 7.3, i.e. not nearly so much as indicated by the changes in the color of the content of food vacuoles which contain neutral red. 10. The increase in the acidity of the fluid in the food vacuoles probably is due to respiration in the ingested organisms, chemical changes associated with their death, disintegration of the ingested plasmalemma, impermeability to acids of the membrane around the vacuoles and diffusion of fluid from the vacuoles. The decrease in acidity is due to diffusion of alkaline fluid from the cytoplasm into the vacuoles. The cytoplasm secretes neither acid nor base. 11. The acid in the food vacuoles probably facilitates increase in the osmotic concentration of the fluid in the vacuole, resulting in diffusion of fluid containing enzymes from the cytoplasm into it. The base promotes digestion. 12. Death of the organisms in the food vacuoles is not caused by acid. It probably is caused by decrease in oxygen in the vacuoles, owing to respiration of the organisms in them, diffusion of oxygen out into the cytoplasm and decrease in the volume of fluid in the vacuoles. 13. The changes in the size of the food vacuoles are probably due to differences between internal and external osmotic concentrations. 14. The hydrogen ion concentration of the fluid in the cytoplasm is approximately pH 7.4.