unit, and the chemist unaided can trace the work no further. A new set of forces apparently comes into play, and whether we say this new agent is vital force, or prefer to hold fast to scientific accumulations of facts and methods of thought, and regard the new mystery as but the result of new or changed conditions, it is equally evident that the province of pure chemistry ceases, for this limit was long ago self-assigned by the science, and indeed exists in a latent form in all its definitions.
Doubtless, either biology, or some as yet unspecified portion of science, drawn from the provinces of chemistry, physiology, anatomy, and physics, will take hold of this problem and solve it; to a certain extent is doing so now, and thus far the little light which has been gained seems to indicate the unbroken operation of uniform law acting through the known physical forces. Perhaps under this heading common gun-cotton offers one of the most striking examples. The cotton-fibre is an elongated cell, it is of course both vegetable and a special functional organ, and is therefore outside of what was above spoken of as the limit of pure synthesis; nevertheless, by the simple operation of immersing it in strong nitric acid, the properties of the tissue are remarkably changed. It has become highly combustible and explosive, and also soluble in a mixture of alcohol and ether. Now, the chemical change has consisted in a bodily removal of hydrogen, and the insertion into its place of a heavy red compound gas, and yet the shape, color, and texture of the cotton-fibre are so little altered that none but an expert can perceive any external change. Moreover, by a reverse process, gun-cotton can be changed back again into the ordinary article. It is, then, possible to most profoundly alter the chemical structure and properties of one of these organic cells without visibly changing its individual shape.
On the other hand, when gun-cotton is dissolved in ether, it becomes collodion, and when this solution is evaporated the vegetable tissue is left, not in its original fibrous form, but as an amorphous film; so here we have the cellular characteristics utterly destroyed by an agent which is not regarded as exerting any chemical action at all; and, by analogy, we may infer that the specialized forms of organized bodies are not therefore the necessary results of their atomic structure only.
Another example of the same kind is the facility by which certain crystals may be made to take on either an amorphous or an apparently cellular form. It is only necessary to add gum, or some other mucilaginous material, to the water in which they have been dissolved, to have them appear, on solidifying in this anomalous way, all their beautiful sharp angles and edges lost in a formless mass or in rounded nodules, like many of the renal and vesical calculi.
But this paper has already reached the limit of facts, and has perhaps entered too far into the region of speculation. In the controversy now going on, as to the spontaneous generation of life, some of