A Value for the Tension at the Surface of a Myxomycete

Abstract

It has appeared of interest to obtain a value for the tension at the surface of a myxomycete∗ in view of the fact that these organisms exhibit relatively rapid protoplasmic streaming. The method used was the oil drop one of Harvey and Marsland. 1 An oil droplet is injected into the organism and is then pulled out by centrifugal force while under observation in the microscope-centrifuge. The buoyant force of the oil is equated to the tension around the circumference of a neck of protoplasm of the same diameter as the oil drop.

Where D = diameter of oil globule, T = tension in dynes, V_o = volume of oil droplet, Δ_ρ = difference in density between oil and medium, C = centrifugal force in times gravity, G = force of gravity, 980.

The criterion of recovery was protoplasmic streaming after the experiment. It was noted that centrifuging apparently stimulates streaming. In almost all of the experiments, as the oil pulled out, a very thin pellicle was visible at the surface of the myxomycete through which the oil passed. The film coalesced again, leaving no frayed edges after the oil had separated. Once the oil starts to pull off the neck of protoplasm narrows very quickly.

The medium was frog Ringer's solution diluted 250 times. Four different oils were used, as shown in the tables. While the differences in values observed are not very great, that obtained using Menhaden oil seems significantly smaller. This may be correlated with the appearance of the oil on injection. In all cases but that of the Menhaden oil, discrete globules of oil were formed of the complete mass of oil injected. The Menhaden oil, however, formed a diffuse injection, and when centrifuged small parts of this in the form of small globules separated out and then pulled off. In control experiments, the Menhaden oil was seen to diffuse uniformly throughout the animal in 20 to 30 minutes, and was then not visible. Subsequent centrifuging resulted only in the separation of a layer of oil on the centripetal edge of the organism, not in the formation of globules which could be pulled out.