Abstract
Urea is slowly but progressively toxic to amebae when added to the immersing fluid. This toxic condition is evidenced by withdrawal of radiate pseudopods, change to unipodal form of locomotion, and, finally, by rounding up and quiescence. If sedimentation of granules and crystals is taken as a criterion of fluidity, it is concluded that the endoplasm is in a state of liquefaction in a high percentage of cases (M/12 to M/48 urea).
Injection of urea into the internal protoplasm uniformly produces liquefaction. The contractile vacuole, thus deprived of a gelated region for mechanical support,∗ becomes greatly dilated. It is usually carried anteriorly, and may be artificially emptied by pressure of a blunt microneedle. Small accessory vacuoles of the explosive type may still function in the gelated area maintained just under the plasmalemma. After injections of strong solutions, the plasmalemma blisters over the entire surface. Dilute injections cause the formation of clusters of uroid-like pseudopods.
It is probable that the liquefaction of the internal protoplasm after penetration or injection of urea is due to the chemical property commonly attributed to this substance, i. e., its dispersive action on colloids.
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