1.) [Illustration: FIG.

1 .-- DIAGRAM OF CELL.1.Cell membrane.2.

Cell substance or cytoplasm.3.Nucleus.4.Nuclear membrane.
5.

Nucleolus.] A simple conception of health and disease can be arrived at by the study of these conditions in a unicellular animal directly under a microscope, the animal being placed on a glass slide.

For this purpose a small organism called "Amoeba" (Fig.