force" thus: "We are at freedom to imagine the existence of a new-agent, and to give it an appropriate name, provided there are phenomena incapable of explanation from known causes. We may speak of vital force as occasioning life, provided that we do not take it to be more than a name for an undefined something giving rise to inexplicable facts, just as the French chemists called iodine the substance x, so long as they were unaware of its real character and place in chemistry. Encke was quite justified in speaking of the resisting medium in space so long as the retardation of his comet could not be otherwise accounted for.
"But such hypotheses will do much harm whenever they divert us from attempts to reconcile the facts with known laws, or when they lead us to mix up discrete things.
"Because we speak of vital force we must not assume that it is a really existing physical force like electricity. We do not know what it is; we have no right to confuse Encke's supposed resisting medium with the bases of light without distinct evidence of identity. The name protoplasm, now so familiarly used by physiologists, is doubtless legitimate so long as we do not mix up different substances under it, or imagine that the name gives us any knowledge of the obscure origin of life. To name a substance protoplasm no more explains the infinite variety of forms of life which spring out of the substance than does the vital force which may be supposed to reside in the protoplasm. Both expressions are mere names for an inexplicable series of causes which, out of apparently similar conditions, produce the most diverse results."
THERE is one more constituent of animal food that demands attention before leaving this part of the subject. This is the fat. We all know that there is a considerable difference between raw fat and cooked fat; but what is the rationale of this difference? Is it anything beyond the obvious fusion or semi-fusion of the solid?
These are very natural and simple questions, but in no work on chemistry or technology can I find any answer to them, or even any attempt at an answer. I will therefore do the best I can toward solving the problem in my own way.
All the cookable and eatable fats fall into the class of "fixed oils," so named by chemists to distinguish them from the "volatile oils," otherwise described as "essential oils." The distinction between these two classes is simple enough. The volatile oils (mostly of vegetable