Note 4 — Chapter VIII · ON THE NATURE OF THE SURFACE LAYER

It is possible that Gruber was led to suggest a gelatinous composition for the layer in question on the strength of assertions made by several writers that amebas secrete mucus. It is true that amebas may be displaced by threads of mucus hanging to glass needles which has collected on the needles while manipulating the amebas in the culture medium, but that is not to be taken as evidence that the mucus is secreted by the amebas. Ameba cultures are always full of gelatinous material formed by bacteria. I have not thus far been able to convince myself that amebas actually secrete mucus.