Osmotic Properties of Oyster Egg Cells

There is abundant evidence that living cells function as osmotic systems (1). Quantitative studies, however, on osmotic equilibria and on the kinetics of osmosis with animal cells have been hindered by lack of suitable material. To serve as osmometers for experimental purposes, cells should meet the following requirements: 1. They should be obtainable as isolated cells of a single type. Cell aggregates, such as tissues or organs are unsatisfactory, since they contain not only cells of more than one type, but also blood vessels, lymphatics, tissue spaces, and intercellular substances--all having different properties. 2. The cells should be free to undergo changes of volume, since osmotic phenomena involve such changes. In tissues, free changes of cell volume are interfered with by mutual pressure of component parts; even certain isolated cells are unsuitable, because of the rigidity of their surface membranes (2). The size and shape of the cells should be such as to permit accurate measurement. Few types of animal cells are known that fulfill these requirements; wherefore quantitative investigations of osmotic phenomena, and of the related property of permeability, have been confined almost entirely to two types of cells: mammalian erythrocytes and ecchinoderm egg cells. In the course of search for new material, the eggs of two other forms of marine invertebrates which belong to different phylathe annelid Chaetopterus pergamentaceus and the mollusc Cumingia telenoides--have also proved well adapted for osmotic studies (2). Unfortunately, neither of these forms were readily available, nor was the number of eggs from any single specimen of Cumingia sufficient for some experiments. Further at tempts to find suitable cells disclosed that the unfertilized egg of the oyster is excellent material. This animal is widely distributed, its eggs are very abundant, and are obtainable without difficulty. To stimulate shedding of eggs, oysters are placed in bowls of sea water, the temperature of which is suddenly raised to 32-35°C., after which the water is allowed to cool. 1 When