Page:The System of Nature.djvu/71

 to unite with more or less facility; whilst others cannot combine or unite themselves: water combines itself readily with salt, but will not blend with oil. Some combinations are very strong, cohering with great force, as metals; others are extremely feeble, their cohesion slight and easily decomposed, as in fugitive colours. Some bodies, incapable of uniting by themselves, become susceptible of union by the agency of other bodies, which serve for common bonds or MEDIUMS. Thus, oil and water, naturally heterogeneous, combine and make soap, by the intervention of alkaline salt. From matter diversely combined, in proportions varied almost to infinity, result all physical and moral bodies; the properties and qualities of which are essentially different, with modes of action more or less complex: which are either understood with facility, or difficult of comprehension, according to the elements or matter that has entered into their composition, and the various modifications this matter has undergone.

It is thus, from the reciprocity of their attraction, the primitive imperceptible particles of matter, which constitute bodies, become perceptible, form compound substances, aggregate masses; by the union of similar and analogous matter, whose essences fit them to cohere. The same bodies are dissolved, their union broken, whenever they undergo the action of matter inimical to their junction. Thus by degrees are formed, plants, metals, animals, men; each grows, expands, and increases in its own system or order; sustaining itself in its respective existence, by the continual attraction of analogous matter; to which it becomes united, and by which it is preserved and strengthened. Thus, certain aliments become