The effect of heat and cold upon the movements is very marked, cold rendering them slow, or arresting them altogether. Heat at first greatly quickens their movements, but when raised to 35° C. it causes them to fall into a state of tetanic contraction and assume a spherical form.

This state is one of heat-tetanus, and if the temperature be now reduced, the movements will again reappear.

At a temperature of 40° C. they also become spherical and motionless. But their movements do not return when the temperature is reduced; they are in a state of heat-rigor, the high temperature having coagulated the protoplasm.

Slight electrical shocks from a coil increase the rapidity of the protoplasmic movements; stronger ones cause tetanic contraction; and numerous or powerful ones produce coagulation.

Common salt in very small quantity (a drop of 1 per cent. solution slowly added) first quickens the protoplasmic movements and then causes sudden tetanic contraction, and the expulsion of any food they may contain at the moment, and sometimes even expulsion of the nucleus.

When water is added so as again to dilute the mixture the amoebae resume their movements.

Both acids and alkalies, when very dilute, increase the protoplasmic movements and afterwards arrest them.

Hydrochloric acid has a more powerful action than a solution of potash of a similar strength. It causes the amoeba to contract and form a ball with a sharp double contour. In it, twitching, movements first occur, which expel any food present. It then becomes pale and lumpy, and breaks up.

Potash causes them to swell up and assume the form of large pale vesicles, which quickly burst.

A constant current of electricity causes contraction and imperfect tetanus; and, if powerful and long kept up, the positive pole produces in the amoebae near it the same changes as dilute hydrochloric acid, and the negative pole the same changes as are produced by an alkali such as potash.

Oxygen appears to be necessary for their life; its removal by means of hydrogen deprives the amoebae of their power of motion, and finally causes contraction and coagulation.

Carbonic acid alone has a similar action to removal of oxygen and produces this effect both in the presence and absence of oxygen, but takes a longer time to do so when oxygen is present.1