The amoeba consists of a small mass of structureless protoplasm, without any distinct cell-wall.

It contains numerous granules and nucleus, with nucleolus, as well as one or more vacuoles, which appear to be small spaces filled with fluid.

Some amoebae live in salt water, others in fresh water; and, although it may be impossible with the microscope to detect any marked difference between them, they exhibit a great difference in their reactions to drugs - the salt-water amoebae being only slightly affected by them, while fresh-water amoebae are readily susceptible to their action.

The amoeba is nourished by simply adhering to any particle of food, closing over it and digesting it, and afterwards opening and ejecting the residue.

This protoplasmic mass is almost constantly altering in shape, pushing out projections at one point, and drawing them in at another. By this means, also, it moves about from place to place.

Method Of Experimentation On Amoebae And Leucocytes

In experimenting on amoebae, take a drop of slimy sediment, such as is found in the tanks of hothouses, and place it on the covering-glass of a microscope; this may then either be put on an object-glass, and the excess of water removed by filter-paper, or, still better, it may be inverted over the opening of a Stricker's warm stage.

1 Rossbach, Verliandl. d. phys. tried. Ges. zu Wiirzburg, N.F., Band iii. p. 346.

When it is simply laid on the object-glass, a solution of the drug is added by putting a drop across the edge of the covering-glass, and allowing it to be drawn gradually underneath by capillary attraction.

Gases are best applied by means of a Stricker's stage, which is also convenient for experiments on solutions.

In experimenting on leucocytes with the aid of this stage, a covering-glass is applied to the cut surface of a newt's tail, or to the surface of a drop of blood, so that a very minute quantity of blood adheres to it.

The drug to be tested is kept dissolved in a .65-.75 per cent. solution of common salt (Na Cl). The salt solution of this strength is often called simply normal salt solution, and is used instead of water, because water itself has a very destructive action on those forms of protoplasm, which are usually nourished by saline solutions, like blood or serum.

A drop of the salt solution containing the drug is placed over the blood on the covering-glass, and inverted over the warm stage as already described. If the experiment is to continue long, a rim of oil should be drawn around the edge of the covering-glass with a camel-hair pencil, so as to prevent evaporation.

The advantage of using such a small quantity of blood is, first, that it mixes rapidly and perfectly with the solution; and secondly, that it does not dilute the solution of the drug, and we thus know the strength of the drug used.

If we used a large drop of blood, we should have to employ a solution of the drug twice the strength we desire, so that when a drop of equal size was added to the blood, the mixture would contain the proper proportion.