THE FOOD-VACUOLE IN THE PERITRICHA, WITH SPECIAL REFERENCE TO THE HYDROGEN-ION CONCENTRATION OF ITS CONTENT AND OF THE CYTOPLASM

¹ The Marine Biological Laboratory, Woods Hole, Massachusetts, and the Zoological Laboratories of the Johns Hopkins University and the University of North Carolina

1. The feeding apparatus in the Peritricha consists of a ciliated tube (the outer portion of which is called the vestibulum and the inner the pharynx) and about ten fibers (oesophageal fibers) which are attached to the distal end of the pharynx and extend as a bundle through the cytoplasm nearly to the posterior end of the body. There is no oesophageal tube.

2. The Peritricha feed largely on bacteria but various inanimate particles are also ingested.

3. At the end of the pharynx surrounded by the oesophageal fibers there is a cone-shaped sac (the oesophageal sac) which consists of a membrane probably produced by the interaction between the fluid in it and the cytoplasm around it.

4. The pharyngeal cilia force into the pharyngeal sac culture fluid with particles in suspension and usually gelatinous substance secreted by the peristome, the vestibulum and the pharynx.

5. The sac enlarges and becomes spindle-shaped. Then a portion of it is constricted off to form a food-vacuole.

6. The constriction is probably due to local simultaneous inward pressure of the oesophageal fibers.

7. The food-vacuoles vary greatly in size.

8. Initiation of the constriction in the sac and the size of the food-vacuole formed by it are not specifically correlated with the size of the sac or particles in suspension in the fluid in it or the chemical composition of this fluid, but they are to some extent dependent upon these factors, especially the chemical composition of the fluid.

9. The concentration of particles in suspension in the fluid in the oesophageal sac increases as the sac increases in size. This is largely due to the passage of fluid through the oesophageal membrane into the cytoplasm.

10. After the food-vacuole is formed, it passes rapidly on a fixed course through the cytoplasm to the posterior end of the body and then slowly on a varied course to the anal spot in the wall of the vestibulum. The rapid movement is probably due to waves passing synchronously along the fibers. The slow movement is due to cyclosis.

11. After the vacuole has reached the posterior end of the body it usually becomes spherical in form and gradually decreases greatly in size; as it decreases in size the acidity of its content increases to a maximum of pH 3.2, then it increases very rapidly in size and the acidity of its content decreases to pH 6.9.

12. The hydrogen-ion concentration of the fluid in the cytoplasm is approximately pH 7.

13. The decrease in size requires about two minutes. It is due in part to excessive external osmotic concentration and in part to inward pressure of the stretched membrane at the surface. The increase in size requires about three seconds. It is due to excessive internal osmotic concentration probably caused by chemical changes produced by the increase in the acidity of its content.

14. The increase in the acidity of the content of the vacuole is probably largely due to the production of acid, owing to metabolism in the peristome, the vestibulum and the pharynx and impermeability of the vacuolar membrane to organic acid, resulting in its retention and consequent concentration as the vacuole decreases in size.

15. The decrease in acidity is due to the flooding of the vacuole with fluid from the cytoplasm.

16. The osmotic concentration of the fluid in the cytoplasm of Vorticella varies directly with that of the surrounding medium. The former is higher than the latter approximately by an equivalent of 0.0125 M lactose or 0.3282 atmospheres.