structure, and further, that every cell with special functions is formed of specially constructed components, is very often met with doubt. How is it possible for the animal and plant worlds to produce such an enormous number of different compounds? There would have to be formed millions and millions of different substances. Only think of the enormous amount of animal and plant species, and just put against this the fact that in general always the same and similar components reappear! In each cell we meet with carbohydrates, fatty substances, and albuminous particles. If these compounds are decomposed into their units, we find the same compounds resulting. All the albumens give, for instance, with very few exceptions, the same, that is, some twenty amino-acids. This obvious contradiction—on one side cell constituents based on similar elements, and on the other the idea of specifically constructed cells—disappears immediately we begin to make a calculation. Suppose we synthesize three elements A, B, and C; we at once obtain, by merely altering the sequence of the particular combinations, the following six different products:—
| A—B—C | B—A—C | C—A—B |
| A—C—B | B—C—A | C—B—A |
If we start with four different elements we get twenty-four different compounds, while five elements
