1. A clot-like material which results from very rapid plasmoptysis and hydrophyllic swelling of karyoplasm of erythrocytes from freshwater fish was reported. This attribute was found to a lesser degree in erythrocytes from an amphibian, but it was almost lacking in those of an aquatic reptile.
2. Rapid clotting of fish blood with the usual clinical methods was confirmed in this work. Fish blood clotted more quickly with the slide test than with the capillary tube test. In the presence of water, complete coagulation of fish blood occurred in only 65 per cent of the time required for clotting to be completed in air. This speed is attributed to the water-erythrocyte reaction, and not to a quality of the plasma.
3. An attempt was made to correlate the findings with the need for hemostasis and blood coagulation that is peculiar to aquatic vertebrates.